I wasn't here in 2008, but seems to me that the emphasis of this site is moving from articles to comments.

Articles are usually better than comments. People put more work into articles, and as a reward for this work, the article becomes more visible, and the successful articles are well remembered and hyperlinked. Article creates a separate page where one main topic is explored. If necessary, more articles may explore the same topic, creating a sequence.

Even some "articles" today don't have the qualities of the classical article. Some of them are just a question / a poll / a prompt for discussion / a reminder for a meetup. Some of them are just placeholders for comments (open thread, group rationality) -- and personally I prefer these, because they don't polute the article-space.

Essentially we are mixing together "article" paradigm and a "discussion forum" paradigm. But these are two different things. Article is a higher quality piece of text. Discussion forum is just a structure of comments, without articles. Both have their place, but if you take a comment and call it "article", of course it seems that the average quality of articles deteriorates.

Assuming this analysis is correct, we don't need much of a technical fix, we need a semantic fix; that is: the same software, but different rules for posting. And the rules nees to be explicit, to avoid gradual spontaneous reverting.

• "Discussion" for discussions: that is, for comments without a top-level article (open thread, group rationality, meetups). It is not allowed to create a new top-level article here, unless the community (in open thread discussion) agrees that a new type of open thread is needed.
• "Articles" for articles: that is for texts that meet some quality treshold -- that means that users should vote down the article even if the topic is interesting, if the article is badly written. Don't say "it's badly written, but the topic is interesting anyway", but "this topic deserves a well-written article".

Then, we should compare the old OB/LW with the "Article" section, to make a fair comparison.

EDIT: How to get from "here" to "there", if this plan is accepted? We could start by renaming "Main" to "Articles", or we could even keep the old name; I don't care. But we mainly need to re-arrange the articles. Move the meetup announcements to "Discussion". Move the higher-quality articles from "Discussion" to "Main", and... perhaps leave the existing lower-quality articles in "Discussion" (to avoid creating another category) but from now on, ban creating more such articles.

EDIT: Another suggestion -- is it possible to make some articles "sticky"? Regardless of their date, they would always show at the top of the list (until the "sticky" flag is removed). Then we could always make the recent "Open Thread" and "Group Rationality" sticky, so they are the first things people see after clicking on Discussion. This could reduce a temptation to start a new article.

yet I can't think of a single topic on which LW 2012 has better dialogue or commentary

Religion.

before LW was OB. before OB was SL4, before that was...

There used to be solitary transhumanist visionaries/nutcases, like Timothy Leary or Robert Anton Wilson (very different in their amount of "rationality"), and there used to be, say, fans of Hofstadter or Jaynes, but the merging of "rationalism" and... orientation towards the future was certainly invented in the 1990s. Ah, what a blissful decade that was.