I think a fantastic thing would be to allow users to redeem their points for "prizes", which could be another user group for X time, or demand a admin-input set of prizes. (Ex: community tshirt, discount coupon, etc). After redeeming the points, they would be deducted the total points they have.
That would keep users "willing to participate".
But i like the idea behind this app and has the potential to be the top #1 app in the marketplace. I'll install it after Christmas.