I had the stainless steel headers on my MX-5 (Miata in your language) ceramic coated to reduce underbonnet temps. Worked very well, reduced heat by 50% and lasted years.
I had gloss black tips grafted onto my Dansk "sausage" sport muffler. I'm told they were powder coated but I'm not sure. Anyway, they have been on for about 5K miles so far with no problem.