I certainly have read lots of things that have significantly helped me make better decisions and have a better map of the territory.
What effect size, assessed how, against what counterfactuals? If it's just "I read book X, and thought about it when I made decision Y, and I estimate that decision Y was right" we're in testimonial land, and there are piles of those for both epistemic and practical benefits (although far more on epistemic than practical). Unfortunately, those aren't very reliable. I was specifically talking about non-testimonials, e.g. aggregate effects vs control groups or reference populations to focus on easily transmissible data.
Claiming that x-rationality can't have big effects because the world is too noisy, just seems like another excuse for avoiding reality.
Imagine that we try to take the best general epistemic heuristics we can find today, and send them back in book form to someone from 10 years ago. What effect size do you think they would have on income or academic productivity? What about 20 years? 50 years? Conditional on someone assembling, with some additions, a good set of heuristics what's your distribution of effect sizes?
LW doesn't seem to have a discussion of the article Epiphany Addiction, by Chris at succeedsocially. First paragraph:
I like that article because it describes a dangerous failure mode of smart people. One example was the self-help blog of Phillip Eby (pjeby), where each new post seemed to bring new amazing insights, and after a while you became jaded. An even better, though controversial, example could be Eliezer's Sequences, if you view them as a series of epiphanies about AI research that didn't lead to much tangible progress. (Please don't make that statement the sole focus of discussion!)
The underlying problem seems to be that people get a rush of power from neat-sounding realizations, and mistake that feeling for actual power. I don't know any good remedy for that, but being aware of the problem could help.