There's a healthy amount of posts here on LW for new users to read, but the wiki is desperately lacking; it's almost all stubs.

I wouldn't want to substitute the best LW posts and comments for equally time consuming wiki contributions. But many of us are incapable of writing the best posts and comments, but I would guess, could do a decent job of making wiki contributions.

And like SoullessAutomaton said:

a well-structured wiki is more discoverable and accessible

One other hueristic I was using - commenting on LW is more fun because it is social, and yeah, the karma helps too. In this context I think this is (weak) evidence that the wiki will be more subject to a collective action problem. Then again, Wikipedia exists.

One possible reason for favoring the wiki, at least in the long run: a well-structured wiki is more discoverable and accessible. The huge branching tree of your OB posts is daunting enough; the entire past corpus of LW is rapidly going to become even more intimidating for lacking a single author with consistent style and themes. Imagine LW at roughly the same rate of content generation and a slowly expanding user base, three years from now. Where would someone even start?

Distilling the ideas into a manageable synthesis of what's been discussed in multiple posts, with extensive inter-linking, terms defined, and links to relevant posts would be far more useful for a newcomer than just minimal definitions with links to posts.

To use an academic analogy, if LW posts are journal articles, the wiki ought to be a textbook.