You could do so much with this. Incorporate an entire economy paying each class of user a different amount. Have them get a paycheck on the 15th and 30th of each month. Since it requires the store hack you could incorporate birthday cards where users can send their own credits, you could also have the board send them a card with credits just for being a member, cards being in the form of a pm of course. You could also do this on holidays and other special occassions.
I also thought this hack should be incorporated with the store
http://www.vbulletin.org/hacks/index...ck&hackid=1032
*edit - Oh yea I forgot to say you could tax them each year too, if the users don't have enough credits you could have the board send them an actual email asking them to check out the board since they haven't used it in awhile. Oh yea and only pay people if they've visited.