What simple and recyclable content would have the largest impact on Spiral Knights' long-term playability?

This is very much opinion oriented, but what sort of small or simple addition would make Spiral Knights many times more replayable for you? Things don't necessarily need to be practical, but shouldn't be too massive in nature.
Small or simple:
(aka what i'm looking for)
- Prestige bonuses (new tabs in featured auctions and supply depot with cycling items)
- UV ticket drops from treasure boxes
- Bring back old prize boxes in the order of appearance alongside new prize boxes, but have them be purchasable via energy bundles
Large or complex:
(aka what i'm not looking for)
- Bomber update
- New levels/enemies
- A level editor with peer review and its own arcade gate of player levels
So taking existing artifacts, what changes would make the game in its current state more replayable? One idea I've had is to bring Apocrea, Kataclysmic Confrontation, and March of the Tortodrones to a cycle where they are active for a week, then cycle to the next event. Alternatively, make the events cycle and only be available on weekends.

Dangit Panda, you beat me too it. But adding onto that, I recently started low level bombing, and I have to say... it's REALLY difficult. Just some re-balancing in bombers favor, especially around the 2* -> 3* area would be great for encouraging bombers. Also some more damage bombs, especially elemental damage bombs would be nice. As of now it's basically status bomb or shard bomb (maybe Vortex).
But yes, plz bring back energy + box bundles again.

I was trying to avoid "add < insert weapon here >", because that will have an impact yes, but its impact would be rather contained. Prestige bonuses are applicable across many areas of knights (namely, after reaching vanguard you now have access to a new supply of items to spend on), as well as bundled boxes giving players options to pay in a way that they prefer.
Another example of a small thing with a huge impact would be to allow shadow lairs to be entered for free, however a shadow key would be required to access the alchemy machine in sanctuary.

Putting back Radiant Sun Shards.
bring back energy + box bundles again.
Add custom lockdown lobbies pls

Small stuff:
Have the three Kat armors (not including Black Kat ofc) not require Wicked Whiskers.
Make BKC craftable in the same way BKR is.
Add back mineral deposits, but not gate building.
Big stuff:
Give all armors that don't provide a bonus (asi, dmg, msi, you know) extra defense to make them actually semi-viable; even moreso if you have a negative effect.
More Poison inflicting weapons.
New Expansion Mission detailing the crash of the Skylark and the Alpha Squad's missions.

Teaching the Game Masters how to copy + paste + change levels in small ways for infinite "events".
That way they can put out rehashed levels like say, shock themed Vanaduke to go along with the shock themed prize box... or T3 jelly king for the slime box, or a free daily mission consisting of an arena followed by a treasure vault. Stuff like that would make the game feel developed and could get the ball rolling again.

Extremely difficult Missions with very tough puzzles that reward the player with unique rewards not obtained anywhere else, and look cool (not the lame crests).

Small stuff
-Revamp compound, making it more rewarding for the time invested, or just give player the option to skip them.
-Revamping some Danger mission with other themes, C42 with freeze, HoI with fire, LoA with more curse and GotM with freeze.
-Forge pass, nuff said
-Hire Ian again to make some more art.
-Daily log in reward, nuff said
-Give the possibility for real gender dimorphism between male and female knights, nothing major, just enough to tell apart. So that way making multiple knights can be more fun.
Big stuff
-Giving LD proper classes like LoL or DOTA2, and can be balanced separately from the PvE aspect of SK
-Give SK a more grim dark theme (it is going there, but I would like to see more) with options for corpses, gore and blood spill.
-Play as a Gremlin with a different story line (one that actually undermines the SK's side of the story) with its own unique player progression.
-Lore extension, add in Morai war DLCs.
-Give SK a proper villain instead of some Saturday morning cartoon bad guys. Swarm is not included as its agenda, or the lack thereof, is still somewhat a mystery.

I was trying to create a parallel as to what I wasn't looking for and y'all keep posting both categories. We see posts on what huge thing should be added all the time, but fairly often those things will only add so much playtime to the game (ie, new expansion mission, new danger mission) but take a lot of development time. I was more looking for what small thing can have a huge impact.
Here's a few responses:
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I like the idea of BKC being craftable. Small change that's pretty much just begging to be added. Could convert the BKC drop to 5 wicked whiskers instead, totaling 6 for the book owner.
I also like the idea of GMs being able to customize levels for us. At the same time, that seems a bit more... Well, "big picture". If they could grab existing levels are make their own "prestige mission" then that would create the illusion of community/dev involvement and be a lot of fun. Graveyard followed by shock complex followed by depth 1 of GitM? Sign me up!
Compound rework is good, and daily log-in reward is good incentive.
I will say the male/female knight thing is prevalent in costume pieces, but not to any such extent that it's exclusive to one gender or another. I really applaud that design choice and would rather that remain.
Another thing Fehzor's post reminded me of was how amazing an entirely random, boss-strata-less gate would be. Don't know what to run? Run the random gate. There can be any (depth) appropriate level on the next floor. shock gremlins one level, fire fiends the next. If the gate map could show what levels you've landed on so you can trace your path however, that would be great.

Oh you touched on something I used to love about SK. One of the most captivating things about this game for me in the beginning was that all the gates changed, and there'd be something new every time. I'd run every gate whenever it came out cause I wanted to see all the levels, patterns, and danger rooms. Skip to about 200 gate runs later, and I have practically every pattern memorized. I don't need to even enter a clockworks room to know what will spawn and where, just the slightest block textures need to be visible on the minimap, and that's it.
If SK can bring back the amazing concept of 'an ever changing world for you to explore' by adding new generic level sets, new enemies, or just doubling the amount of rooms you can encounter in clockwork tunnels, PvE would have it's luster again.
Another thing that just popped into my head; crafting Rarities with Minerals. :3

There is no answer. There's no small or simple thing that could be changed that would make it long term playable for me, well, adjust the heating system a bit perhaps? Despite not being required to level 5* items for any practical reason like crafting, I would like to not have to see the little notification on my forge icon. But that wouldn't make it replayable, that's just QoL. Replayability for the most part requires long term developed content.
THOUGH, I do like the daily login idea. we do get daily things already, the prestige missions, but prestige has no real value or affect on our gameplay. I would LOVE crafting materials to be included in the daily rewards, my biggest issue is crafting low level items right now, simple, advanced, and expert orbs I am missing more often than I think I should be, so as long as those are included somewhere to have a reliable form of long term crafting, I'll be good with that.
EDIT: adding to what Gianor said, the gates just seem too familiar now. I loved the Dreams and Nightmares just because it was unfamiliar. But this is the kind of long term developed content that we just aren't getting.

Having Radiant drop rates go up as your Prestige levels up would bring me back, yeah. That's my #1 gripe about this game's design.
Frankly, I think this game is in a completed state. (AKA what you'd see in a store, etc.) That's why we see few major updates. And yes, it's an MMO, but heck, you know, developers like Nick move on. Anyway, yus Rads plox.

Having Radiant drop rates go up as your Prestige levels up would bring me back, yeah.
I've never heard this suggestion. It seems to be a nice way of killing two birds with one stone: giving a purpose to prestige, and increasing Radiant drops rates without making them too ubiquitous and easy. There would be some details to work out, of course.
Frankly, I think this game is in a completed state.
At this point we can't really know whether that's true, but I've been telling players to adopt that view for years. If you don't expect new content, then any new content is a pleasant surprise.
Most of you who post here religiously have been playing Spiral Knights since its inception, if not earlier in the Beta. That being said, I find it strange that people still want Radiants after 4-5 or so years of playing this game. After all that time, I imagine all of you veteran players would have used/owned every weapon in the game already, or at least a variant of the many that are clones of each other. There are only 7 unique swords, 9 unique guns, and 6 unique bombs in this game (I might be wrong on the numbers, but it's really close if I'm off). It wouldn't even take a year to get all of those and have tested them and played with them enough to know what the fuss is about.
I'm assuming you're seeking out different gameplay options by getting some of these weapons, but most of them are just clones so I don't get it. I'm not a collector. I use the most functional items and have the others on reserve as trolls or something. If this is related to collecting them all, Pokemon-style, than I kind of get it. If not, then I really don't understand how you haven't done everything this game has to offer already, considering the time.
Sorry I can't add to this topic. I was just curious why Radiants are always a concern considering older players should have completed their to-do list ages ago. Anyways, proud of you dudes for keeping this game alive on your own. I've long since gave up, but you guys are hardcore. Keep up the good fight.

@The-Fire-Champion
The reason for wanting radiant fire crystals to be more plentiful extends far beyond personal greed in terms of items. Yes, I have just about everything and for me getting the crystals isn't a problem. It's solved. I can get an item in like a day or two no issues.
The thing is that for newer players and those with the grind ahead of them the game feels awful, daunting, and impossible and so they leave. They lack skills, gear, guides to help them, and most of all a community set up around grinding for radiant fire crystals. They have to find someone like me to grind with, and well, players like me don't play that much because the game is stagnant and we've done everything a good hundred times already. Alternatively they could find Fangel, but there is only one Fangel to go around and I need them for when I log in. If they made more missions viable to grind it would at least make it palatable when you do find people etc.

Right. I do not want the Radiants scarcity fixed for myself. I want the scarcity fixed because it seems to be discouraging new players, and I want Spiral Knights to have lots of new players.

Frankly, I think this game is in a completed state.
There are 3 major things that make me disagree with this statement.
1. Weapon/class balance
There are currently roughly twice as many guns as bombs or swords, and guns are the only truly complete weapon set. There are support guns with plentiful status, guns with high damage, guns with high damage over an area, everything. Guns have a full set of armor to go with them as well as Seerus, making them an alpha class.
For the game to be in a completed state, it would need a sword and bomb update to go with the gunner update.
2. Armor balance (And other 'vestigial' features)
Currently, there are a massive number of redundant armors that appear to be vestigial features left over from the game's beta. In turn there are two 'alpha' armor sets = chaos/black kat. These alpha sets completely destroy any semblance of armor balance, allowing your knight to become near-optimal in a world that should do everything to avoid any sort of being optimal.
Other features like this include sleep status, which is kind of in the game as you can be weak/resistant to it but also kind of absent. Another example would be how moonstone and valestone are usless but still present and coded to show up more/less often on certain areas from when we built gates. Generally speaking, there are A TON of these loose ends poking their way through.
3. The story isn't finished..
It leads straight into a cliff hanger. But we're still hanging around, waiting for some sort of conclusion.. and there just isn't anything coming? That would be like if JK Rowling refused to write the last Harry Potter book or something.
If they're going to call the game finished, they need to finish it.

There are other things I'd like changed but bringing back old catalyzers is one of them. I just really like the concept of really slow bullets that i can then mix with fast ones from another gun to confuse opponents. The only option right now is pola (or another pulsar-line gun) and that gun is just too broken to be used.... oh, I guess I can come up with one small thing I'd like to change. There's a gun line that should somehow be nerfed....

Armor/weapon balance would do the game a solid, but I'd also like it if getting them wasn't such a massive time investment.
If it took half the time/energy to get a 5-star piece of gear up to max, I'd invest more time in trying to collect more of them. I think that having such a wide variety of gear, and the incentive to get them, would be fun in and of itself. It'd buy more time for the devs to work on other things, anyhow.

Larger instances (more than 4+ to a party)
Roaming bosses
These are things that certain aspects of the game already has but with a simple tweak would easily make the game waaay more enjoyable.
They could easily change the way you get into matchmaking for PvP by having party formations and issue of challenges that show up in chat or notices (like party invites) alternatively to queuing for a match.
Simple
--Armor
I want a cold iron vanquisher armor set with some cool chains floating and one eye glowing effects + a special shield that if charge bashing it will shock the enemies
Complex
--Levels
More family enemies that can be only found in arcade to encourage players to play in arcade+more arcade only generated levels
Add mini or special levels in arcade in which you pay a small fee to participate this special levels contains special tasks such as defeating specific rare enemies or helping an attack gremlin or knight from enemies(they will help you or you will need to protect them like a defend the tower type of game) if successful you will be highly awarded with rare and unique reskins models of certain armors,gears or weapons.
Clean up of game animations and collision bounds and fix some of the weapons in the game(eg bombs,winmillion and torto weapons)
--Enemies
Add more enemies for each family + allow player to cancel bullets from enemies when in contact with charge attacks or attacks stronger than the enemy's bullets

May I put forth for your consideration this event idea? If you take out the crown part of the idea it would give an entertaining, fun, useful activity with almost zero effort from OOO. :D
(If you like it, please +1 this idea)
--Chesh

Just make sure that any of the events that you propose actually provide adequate farming rewards. The evidence I've seen has shown that a reduction in such has lent to people quitting sk. I'm still requesting that they rebuff drops at vana/shadowplay/DaN, since the indirection and time taken seems like a gameplay killer.

Increase the current itemdrop (armor, helm, shield, weapon) rate. It would be actually fun i think. Even if most of the time you would get items you actually would not use, still would be awesome ^^
Also some cool ideas have already been written, i wont repeat those.
Edited offtopic: I know you did not ask for big gamechanges but i'll still write one :) Observer/Coach slot implement into PvE parties. A player who actually doesnt have his knight playing, but could still be in the party, and kind of only observing, or advising to the others. I think it would be great.

I remember getting a 5 star skelly helmet/armor/shield once every two months at vana prior to the 2013 pet update on an older character. Seems like drops stopped for a year, then got "partially" reinstated after enough people noticed and complained.
@Fangel
They need login rewards badly to keep people "in" even if it's just for 5 minutes a day.
+1 to prestige rewards.... maybe the type of login reward you get could be based off of prestige?
They need to buff up rad drops at vana heavily, and advertise it like it's some sort of double xp weekend, and do it once a week or month. Maybe do it when there is no event, to keep numbers and focus changing each week.

Yeah the login reward is a simple and already well working system in other games.
So it is a really good idea.
As well as the "weekend deal" idea.

Daily login rewards. It's so
that I am shocked I've never seen it suggested before.obvious
With the old Mist system, THAT was like a login reward. And after that people stopped needing to log in so often.
It would be reasonable to implement, too. OOO can send out a mail each day with a random item to each person. At the end of the day (maybe when the gates change?) they pull all of those mails out of everyone's inbox, opened or not. Then send out new ones.
Yeah. SK needs that. Definitely.

Pretty much the same idea here.
Examples
Randomly getting one of theese:
- 1 spark of life
- 1 alchemy orb (random star)
- 10 fire crystals (random star)
- x petfoods
- y materials
- z crogmo coins
- common tokens
- one trinket or weapon slot
- etcetc
They need to be bound of course.
I love the idea that prestige increases crystal drops, as I have to admit thats by far my biggest problem with the game is how scarce rads are. Even on D28 and elite difficulty it seems 1/3 of the crystal drops are shinings, I actually played through a T3 gate in arcade and came up with only 3 rads, thats just way too low consideiring 5* items require more crystals than any other level.
The log in rewards is also a great idea, maybe random things such as 30 crystals of your level type, an orb, a uv ticket, a 2* item, etc. Weekend rarity drop increases is also pretty genius, sometimes it makes me wonder why some of you haven't been hired yet because a lot of these ideas are fantastic.
Putting back Radiant Sun Shards.