Second caveat: In this scenario, collusive voting behavior can generate more financial reward, so guilds may start to exert more power. I don't see this as either good or bad, just something that we should account for, one way or another.
this is incorrect. It would actually generate less. Additional users "piling on" would see diminishing (instead of exponentially increasing) returns. The curve becomes more linear as the support grows.
Incidentally, your first caveat is somewhat suppositious. You could make as compelling an argument that people would be inclined to spam low quality posts as a way of buying a "lottery ticket" at a chance for one exceptionally high paying post. The only system where there would not be a perceived incentive for posting more was one where there was no perception that the posts has any chance of getting rewarded at all.... which would obviously be a bad one.