I still got stuff out of it during my PhD (in mathematics, though I never finished). I think you might underestimate the value of tacit-knowledge-type stuff, especially from skilled mathematicians like Polya. It's interesting to see how they tackle hard problems, and to compare it to how you would do the same - at the very least I have a much less developed philosophy about it. Terrence Tao has blog posts about his problem-solving meta as well, that are interesting (to me) for similar reasons.