Do the gates still seem too similar?
It still seems like Shock and Poison are the most common strata, and not just by a little bit: red and yellow minerals specifically are lower across the board on like every one.
Is it just because red and yellow are less often bigger than the others, so people don't pick them up? : /
I only pick up Blues and Darks since they're prettier.
Yellow, Red, and Green only when Blue and Dark are smaller.
99% of the games population either has no clue how gate construction works or just doesn't care and will pick up whatever mineral is the largest even though the payout for minerals is so little.
I wanna see more Gremlin/Proletariat-Slime/Undead/Fire Stratums. Hell, I'm even starting to miss Beast.
... Actually, maybe I just want to see a slightly reduced chance of Clockwork Tunnel and Deconstruction Zone stages. I might bother with entering a shock stratum if it had something besides those. SO TIRED OF THEM!

Is it just because red and yellow are less often bigger than the others, so people don't pick them up? : /
I've never noticed that before...
Anyway, whenever I'm in a group I try to get the biggest minerals I can find. This allows the team to get the most minerals possible. If there are two minerals of the same size I'll go for the color I want (usually Yellow > blue > green, but it can change depending on what the team has and what mood I'm in..)
Because of their common-ness, Blue and Purple are worth the fewest crowns.
It is actually the same amount of profit taking a large Yellow or Green mineral (3cr x 4 mineral) as taking a huge Blue or Purple mineral (2cr x 6 mineral).
If you see two minerals of the same size, favor the colors that aren't blue and purple. You'll get a bit more crowns out of it, and contribute to reducing the mass Shock/Poison epidemic.
I'm not sure how construction works I have a basic idea, someone want to clue me in? Fill me in, and ask me if you want any help with the construction of certain gates, I'm interested in how it works and what I can get from a new gate :) I get tired of familiar worlds too.
Maybe a community project can be made like one I've heard before where someone rallied everyone to make an all-Jelly gate. :3
Is it possible to make an all-boss gate as well (Smarbalox, Jelly King and Vanduke-whathisface)?
Players have no control over when a boss stratum appears in a gate. It'll already be in the gate before it's constructed.
As for how gate construction works, look here. Ignore the stuff about strata getting full, because that doesn't happen anymore. I guess the wiki is a bit out of date. There's also an NPC in the arcade that dispenses most of this information after you do some stuff for him.
Whenever I see a poison on the gate I'm building, I pour all I got into it in an effort to change it... *thumbs up*
The poison is somewhat okay. The shock is NOT okay. Learn thy enemy.
I actually hate all the elemental stratum. They're impossible to gear for other than "do I have that resist" :P

They're impossible to gear for other than "do I have that resist"
And, y'know, Elemental Defense.

I always take the biggest minerals available, with a preference on green yellow and red over blue and purple.
BUT I carefully choose where to put them, avoiding for example to help Shock creation after 3rd stratum.
Also don't hurry to put all your minerals in gates after every run, keep them even in large stocks waiting for better payouts and "safe" strata to put them into (e.g.: keep all your blue and purple minerals waiting for a low stratum with a big payout for them)
I'm pretty sure it's because minerals in the recipe for creating a statum don't appear as often within the stratum itself. Therefore, blue and purple are the most common minerals in a jelly strata, and lots of people run JK for money, sooo....
...or maybe people are just idiots. That's always possible.