I was a Free 2 Player, that worked his way up to 5*. It was a long and grinding road, which I believe lends some credence to the following suggestions.

First of all, I want to say thanks for making Spiral Knights the fairest F2P system out there. It took a while, but I was able to go all the way without spending a dime, and access all the content (well, up until shadow keys). I never felt disadvantaged because I hadn't spent money, and I helped make the economy work by driving up the CE value for the paying customers. I have since "bought in" to get past the effective pay gate of the shadow key prices, but I am not resentful. The shadow keys were ridiculous, and OOO presented a solution that temporarily alleviated it. Yes, only a temporary solution, but all the people that wanted to access the content could, and by now the general consensus is "not worth it" so demand has dropped.

Anyway, on to suggestions!

1) Make a way to change your color. I will admit it: I joined because I wanted the TF2 hat. I hit the random button on character gen, and played until I got the achievement. Once I found out that this was basically co-op zelda, I was hooked, but I put no care into creation. Now, like millions of others, I am bright red, and being able to change that would be nice.

2) Take a look at some of the weapon balances. I <3 Troika, but sealed sword upgrades are basically better in every way. I really regret working on a Triglav, because the fact that enemies that freeze aren't knocked away really hurts the reliability of the sword, and the damage output is just so much lower than Divine Avenger that I never feel like bringing it along. That, and the charge attack is basically suicide, since you have a full second of vulnerability where you cannot act. Think of it this way: If weapons besides the Barbarous Thorn Blade, Gran Faust, Divine Avenger, and Leviathan Blade become viable, there will be more interest in people bringing these up to 5*, and thus more CE drained in crafting costs. I really enjoyed my Volt Driver until I found out that the bullets did the same damage as an unprimed Gigawatt Pulsar.

3) A "Lending" program. Say you purchase a 50 CE "Lending" pass, which unbinds a sword for a day. At the end of the day, it goes back to its owner. This lets high level players with a bunch of spare CE help teach their guildmates what weapons to use, and gives the less experienced players something to be excited over. I got a friend hooked as well, and he was always disappointed that he was stuck doing Tier 1 runs while I was running the "exciting" stuff. I could easily give him 2* gear, but beyond that, it was cost prohibitive.

4) New bosses. I admit, the game is starting to get a little stale. You can only run FSC every day for so many weeks before you get bored. I really, really want to fight in a Tier 3 Gremlin boss level. King Tinkinzar, ahoy. Or see a Tier 1 fiend boss (please Tier 1 for this, because fiends are too scary at higher levels).

5) New pickups. I am, of course, proving my ignorance, but I can't imagine that some new pickups would be too difficult to add. How about a strength booster, that gives you a Sword Damage: Medium bonus for 10 seconds. A mystery vial, that provides two random status effects when it hits. The goal was to make this more roguelike, right? I find myself usually heading back to haven with a full load of potions, and I would like more incentive to use them.

6) Remove the friendly fire from mechaknights. I just love waiting around for a gate to change, and getting killed because one of my teammates spawned a mechaknight, it stood next to me while I was going to the bathroom, and shocked itself, and me. I have never payed 5 energy to turn one of these menaces on, and I never will.

7) Easy heat sharing. I am assuming that heat sharing is acceptable? So why make us go through all the trouble of dying? Make heat sharing like an elevator tab.

8) Reform the party join requirements. I understand the goal was to stop arena looping, but let me present you with the following scenario: I quit from my party at the end of 22, and head down to the crossroads, with the intention of filling my party with guildmates. When I am finished loading, low and behold, I forgot to lock the party, and now I have a random stranger. If I kick him, suddenly my party is locked again. Can't we just change it so that it takes 3 people going solo off of you, for example, before it locks? Still prevents arena looping, but it makes errors like this less frustrating.