I don't think communities should directly rate the content. With more people the general consensus on what is good and what is bad becomes so subjective, to the point where it's what the user's that just happen to see it end up defining it as either "good" or "bad". Instead, the webserver should simply watch the activity levels of all content, including things like whenever a user hovers over a link and for how long to things like replies. And based on all of the available information it should give it a numerical value defining it's influence on the community. It probably can't be 100% accurate, but it can be pretty close and most likely better than what is in place in most communities.