You can "like" or "dislike" your friends' stages. And if roses get thrown onto their stages you can swipe them for cash. Aside from that, well, it's just looking around to see what others have done. Oh, and there are achievements for the number of friends you amass, so get get some sort of reward for that too.
I've leveled Zoot up a lot too. He earns quite a sack of cash between sessions, doesn't he?