Right now, for instance, it's easy to create an arbitrarily high-signal version of LW by going to http://lesswrong.com/prefs/ and changing the thresholds for minimum post/comment scores.

Uh, did not know that. Thank you!

I still have a caveat about posts which are extremely good at getting upvotes having a tendency to be shallow in content, but I think that overall, you are correct.