Some new level ideas that I pondered (because they sounded fun to me) ...
Clockwork Countdown:
Begins with a party-wide button to open a gate into the area. The moment it's triggered, at the other end three gates open up by the elevator down with rooms of boxes similar to the reward for each stage of the arena. The party must try to get through the area as fast as possible (having to hit switches to open doors and do puzzles/party buttons as well as fighting) because each of the gates is on a timer that will close, progressively reducing the reward. The player/groups will reach a final party button to open the way into the elevator (which will also stop the reward gate timers).
Road Not Taken:
Stage is composed of a series of branching paths which finally split into 5 distinct roads that converge back on the elevator. Each path begins and ends with a (single person) button that, when pressed, closes the path back locking them into the path they've chosen. One of the five roads includes a room of boxes and two include minerals. Players have to decide which path they'll take, if they want to split up (and risk fighting nasty stuff on their path alone) and try to predict which paths will offer rewards.
Lastly, the idea that is currently the least feasible:
Team Cross:
A stage that releases two teams against each other in a race to the prize. Not a PvP challenge so much as a competitive obstacle challenge. Any of the regular stages would work well.
And a few interesting concepts for new obstacles/traps.
Ice vents - Vents from the side and below which freeze players in a room with hard-hitting monsters.
Sliding paths - Stepping on the path will cause players to slide down them.
Protected Fuses - A series of gates and/or obstacles powered by an electrical system linked to fuses that must be broken to depower them.
Mimics - Monsters that look like boxes/bushes/breakable stuff until you approach them.
I really enjoyed reading this thread, until I got to the last line. You proposed some very interesting and ingenious ideas that were surprisingly fleshed out. I was glad to see someone actually thinking about placement of triggers and buttons in relation to the stage type. Some of the obstacles/traps were also interesting, but reading the last line made me fume. Mimics? The most overused MMO(RPG) element out there? Really? I am so tired of them! All they do is increase general anxiety. Plus, since you can't actually shoot bushes, you'd HAVE to get close enough to hit them. The one thing I COULD see as a potential benefit would be people using actual guns for once, instead of just dual swords. Other than that, I cringe at the idea of mimics...omnomnomRAGE!
But seriously, a treasure hunting level would be cool...you'd have to explain the level type before the first button, and then wait to start the time until the first team button is pressed. That way everyone KNOWS it's a race and some noob doesn't just go through it at snail pace while you all wait at the button...