If you want to make LW livelier, you should downvote less on the margin... downvoting disincentivizes posting. It makes sense to downvote if there's lots of content and you want to help other people cut through the crap. But if there's too little it's arguably less useful.

Also develop your interesting thoughts and create posts out of them.

Check out metafilter.

Its survival is in doubt. In particular, "The site is currently and has been for several months operating at a significant loss. If nothing were to change, MeFi would defaulting on bills and hitting bankruptcy by mid-summer."

This question occasionally comes up on #lesswrong, too, especially given the perceived decline in the quality of LW discussions in the last year or so. There are various stackoverflow-based sites for quality discussions of very specific topics, but I am not aware of anything more general. Various subreddits unfortunately tend to be swarmed by inanity.