I don't care about IQ, I think it's a fairly uninformative number. Doing proofs eventually gives you a nebulous thing called "mathematical sophistication" (what I sometimes call "metal struts in your brain") that I think helps enormously for adapting to and solving novel technical problems.
When Heinlein said "specialization is for insects" I think he was making a similar point about metaskills.
I don't mean IQ as a number, I mean the underlying g.
And people who graduate college and start working neither do, nor are expected to "solve novel technical problems". The closest to that are programmers who do have to solve problems daily, but for them courses in e.g. data structures or just experience with radically different languages will develop much more useful intuitions than "mathematical sophistication".
If you are going to become a mathematician or a logician, by all means go study proofs. Otherwise I don't think they justify ...