This feels like a demographic problem of a larger population dragging down the average. If that's the case, then some sort of curation (vote-weighting or otherwise privileging certain users' input over others) is probably necessary, because the overall level of dumbness, meanness, or mediocrity just isn't going to change that much in response to anything HN does. (I'd much prefer to be wrong about this. Any elitist solution seems regrettable.)
I wonder if this could be tested. Even something as simple as http://news.ycombinator.com/classic applied to comments would be interesting. Or let PG pick, say, a hundred users and let each of them pick an additional two or three. Could the software show us the site as it would appear if those users' votes counted for more? It seems to me it wouldn't take long to get a feel for whether it had helped or hurt.