Ask HN: How to stave off decline of HN?

I was just asking RiderofGiraffes if he had any suggestions for fixing the decreasing quality of comment threads on HN (http://news.ycombinator.com/item?id=2403449) and it occurred to me that I might as well ask everyone.

Anyone have any suggestions? We're on mostly uncharted territory here.

The problem has several components: comments that are (a) mean and/or (b) dumb that (c) get massively upvoted.