The well-kept garden thing obviously hasn't succeeded as planned, so should we be aspiring for some kind of 4chan for rationalists?

I disagree; LW has succeeded far better than, say, SL4, and better than OB. Despite having just a tiny fraction of the population and activity and a heavily restricted set of topics, SL4 was a much less pleasant forum to use.

I wouldn't mind seeing an experimental sub-reddit here that made all comments anonymous while keeping the voting, so that you get some of the benefits of anonymity without being as noisy as 4chan.

4Chan isn't all that special. It's wildly popular, sure, but most of that is because of first-mover advantage: it was the first English-language community with the right incentive structure (in particular, normative anonymity, easy image insertion, and fast-moving auto-expiring threads) to hit critical mass.

I don't think the initial core community of anime perverts has all that much to do with its eventual culture, either. Certainly if it had been seeded with a different type of American geek we'd have ended up with something pretty similar, albeit with more naked pictures of Dejah Thoris and fewer of Rei Ayanami; but I don't even think a counterfactual 4Chan for fraternity bros would have looked very different, except of course that bros don't spend enough time at their computers for that to work. 4Chan's format doesn't provide any enforcement mechanisms strong enough for the seed culture to shape its evolution much, so what we're seeing now is more like the middle of an attractor defined by the incentives embedded in the format.

so should we be aspiring for some kind of 4chan for rationalists?

For making good posts, what kind of pr0n should we reward rationalistfags (ratfags for short) with?

X-D