I feel like spending time learning "domain specific knowledge" is much more effective than "general rationality techniques".
However, reading Lesswrong is what prodded me towards getting better at spending my time effectively, really getting into a growth mindset. My only problem nowadays is that there are too many things I want to learn, and that's a much better problem to have; I know I can, I just have to pick and choose. I'm getting better at that, too.
Maybe the same would have happened anyway, but I don't think it would have happened quite as fast.
I feel I've learned a lot about problem solving from less wrong (and HPMOR in particular). be concrete, hold off on proposing solutions, et cetera. The effect*, unfortunately, doesn't seem to be as much as I had hoped.
Small increases in intelligence are extremely general and even recursive, so it feels worth the effort. But, I found alternatives much more effective (though still modest) then studying/discussing/applying the sequences. like meditation or smart drugs.
I'm interested in other lesswrongers experiences in cognitive enhancement.
* by "smarter" I mean "better at problem solving", where examples of "problems" are writing a program, finding the right thing to say to resolve interpersonal conflict, memorizing some random fact quickly and then recalling it quickly/vividly. let me know if you want further clarification.