I think the furthest I'd take it is allowing users to vote on a post's value, and if the ratio of negative votes to positive votes is too high, then the post fades into the background or hides itself.
In my own experience, posts that flag themselves as worthless draw more attention than bad posts presented normally. Besides, I like formulating my own opinion by reading what someone has to say.
I'd be open to this form of moderation if I put a switch in the preferences section that lets users turn it on and off. I think if it can be completely disabled, this idea has merit. I'll put it on the list (but kind of near the bottom, so don't expect it in the next update).