I'm not going to get into the whole discussion about the 50\50 system because, to be perfectly honest, I'm not the right person and I don't know the system well enough to have a strong opinion about that. I'll just say you make some good points.
I will, however, say that the downvote pool seems a genuinely bad idea. So bad that even with facebook they never came around to add a dislike button, regardless of how many users wanted it. I can see how someone would abuse of a function like that if acting with malice, but I can also see how someone could inadvertently damage the whole system with it; it just starts with a downvote under a post that I don't deem constructive enough, or interesting enough, or incompatible with my religious\political\ethical views. After a while we're gonna have users running away rather then trying to be effective creators (which is already hard, because you need to have something to say, you need to know how to say it and you probably need to have some powerful friends).