That's a rather abstract question... Here I was talking about financial rewards, and influence at #4.
Reputation is another kind of reward; both the formal number and people's opinion of a user. I wouldn't call average post quality or feeling part of a community an individual reward; that's a subjective common good, not a property of an individual user.
I didn´t understand very well the second paragraph of your comment ;)
But anyway... I think our big challenge is that the product we are dealing with has a lot of emotional values. Content is always the result of a creative process. People feel personally touched by the success or failure of their outcomes. So I think a purely rational and algorithm-driven rewarding system won´t ever fulfill their needs.
I agree. I'm happy that financial incentives make us more polite than Redditors, but not everything has to be based on algorithms and money.