I have had exhausts/extractors wrapped, painted and ceramic coated on various cars. The only one that had any effect was ceramic coating - albiet only until it cracked and crazed.
Wrapping, whilst reducing the radiant temp, actually increased the extractor metal temp and promoted rust.
Painting just burnt off in weeks despite being rated suitable to paint the sun
The ceramic I used was Jet-Hot hi-temp. It lasted about 2 years of hard work before it cracked and crazed, but it reduced radiant temp greatly and the extractors didnt expand to greatly from the metal temp.
http://www.jet-hot.com.au/