Wagawiki is kind of like that. Everyone can contribute.Clay, have you thought about having user-created lessons, with awards being prescribed to the best submitted ones?
But you brought up an idea I've been wanting to do for some time: Some sort of TJP contest.
The winner(s) could get gift certificates from TheJapanshop.com or...? I wouldn't mind having a grand prize of $100 or several smaller $50 prizes. (granted not a huge grand prize, but we are a very small business )
I thought I'd made a post asking for ideas for a contest.
BuddhaGeo's suggestion is a good one, but any others? Something that would enrich the TJP community. Graphic art, poetry, or some other member created content? (Eventually once we get the video site moved over, that could be a fun contest medium.)