The problem, as with all great communities, seems to be the abundance of new users and, thus, the widening of scope on submissions and comments.

To me, it seems obvious that to improve HN, the community needs to stop expanding as much and get its main user base back to a niche.

The only tried and true method (that I know of) would be to follow Something Awful and start charging for an account. Something trivial, like $2, would be fine.

Of course, this will never happen. This isn't really something I want to happen, but, to me, it seems to be the only way of limiting the user base in an effective manner.