I wouldn't play, but I think it's a great idea.
You not only supply your members with a little excitement, you encourage them to accumulate more acorns by contributing to the site. Good idea!
And I don't think it needs to be "fair" to all members. Not if it is considered a reward for participation in helping you build the site.
My favorite saying is, "You get out of something, as much as you put into it." Whether it's a pet, a marriage, an education, or a website.
