If you haven't seen the video of the Roadkill Garage guys on Enginemasters dyno test of ceramic vs uncoated vs painted vs. wrapped headers, it's worth the watch. I don't believe they tested ceramic inside the headers just outside, but the net scientific result was it does close to nothing to keep heat in the headers (~10F degrees IIRC). The only somewhat appreciable difference was using the unloveable fiberglass wrap.
https://www.corvetteforum.com/forums/c3-general/4667860-do-header-wraps-work-engine-masters-s7-ep10.html
If your goal is to keep the exhaust looking good and easy to clean, ceramic works great based on my buddy's 3.2 with ceramic coated headers and muffler.