Ok, so here's some more. The most important points?
-TIME: You need to go in. And get out. The longer you're in there, the less power you have (and more you need) and the lower your community's power sources get.
-CHALLENGE: There needs to be a clear challenge, probably on both a player level and character level. Failure should have clear consequences, and the GM should not be afraid to push. If there is a GM. I'm still not sold on the GM.
-LOSS & TRAGEDY: Every time you go down, there's a chance that someone you care about will be hurt by the miasma or the monsters while you're gone. But if you don't go, they'll be hurt anyway. And every time you go, it's riskier.
I'm not quite sure how to actually achieve these points, yet.