One of the biggest issues at other communities was people making a post purely to increase their post account by one, sometimes in very important topics or topics where an interesting discussion was taking place. So you'd have to scroll through layers of muck to get to the interesting part.
My suggestion is to implement a rule for moderators to enforce - no post can be made in a topic which completely restates a point already said intentionally that is clearly made with no effort. Basically, if a topic has been about the intricacies of an organized Russian mafia and how to portray it, somebody shouldn't barge in and say "I know there's some Russians in New York!" or something really irrelevant.
Obviously, this isn't going to fix the problem entirely, but level-headed people will follow the rules.