Yaay incentives to donate~ I think many people would donate JUST for more pixels alone. Even if it was just for $5, i can see more than a handful doing that. My 2 cents:
Reasons to become a "Premium Member":
1) Increase size for avatar
2) Less "exposure" to ads? If possible?
3) Cool little premium medal icon?
4) Extra lines or restricted to 1 image/more balls in your signature?
5) I don't think you'll need "special forums" like srk, but hey, if people want a "general talk" section, they can throw a few dollars in just to type in there. So only premium members can view and see these forums, but don't gain post counts? Just an idea!
6) Support Dustloop stuff!
Additionally, i don't think the rep stuff will be added either, so i'm not too worried! I always thought it was a silly idea.