When I saw the price on all the headers out there I was surprised that they weren't coated already. Coating the header made a huge difference on the engine bay temps on my 240z.
I never used to coat my headers but I read if you do you gain some horsepower. Not a lot, but some. So I did for my 2015. Here is a link to a test that was done on a coated vs non coated.
I did a header on my Honda with ceramic coating at a place local to me http://www.spcoating.com/index.html It looks as good as the day I put it on several years ago. No color change, no rust, no chipping, nothing.