The problem, though, is that what the rationalists will probably conclude is "there's no solid evidence, and it seems likely that any advice works well for a subset of the population and hurts other subsets of the population. You should quantify yourself and experiment."

Which is advice that people are going to have a hard time taking. Giving up specialization of labor is rather hard and rarely worth it.

Now, they might find a few gems- like "you should figure out diaphragmatic breathing"- but it'll be hard to separate those from fads or overbroad advice ("this diet agrees with my evolutionary views, thus I suspect it's good for everyone").