Ask HN: Has anyone put thought into the degradation of online communities?

We've all seen this happen before. You discover this nice new website where there's interesting content and people (let's say slashdot). As more and more people join in, the quality of content/comments gradually starts to decline. Now there's people cracking the same tired jokes/memes over and over again. The people because of whom you signed up there in the first place lose interest and start to leave and that's the end of that. Another ex: Google+ just a few months ago was a place where everyone put an honest effort into making a comment that would be of some value to the reader. The amount of noise there too is quickly catching up to the signal.

I think if you've been on the internet long enough, you've probably seen at least one small online community grow rapidly and then blow up. Has anybody put any thought into how this may be avoided?

HN's is by far the best system[1] I have seen this far but I haven't been here long enough to know if things have changed significantly with time.

[1]write down super specific "guidelines" so everybody's clear as to exactly what is expected here.