Header Wrap - Good or Bad?

Anytime you heat up metal you have hydrogen crystallization, its normal. Trapping heat in exhaust can intensify this effect. You are riding a 600cc or 750cc motorcycle, and if anyone tells you you are going to get better performance from "scavenging effects" or temperature gradients on bikes of these size built for cruising,  it's not something you would notice unless you are trying to shave 1/10 of a second off a 1/4 mile time. The perceived benefits of this are far outweighed by the negative effects of wrapping your motorcycle exhaust. 

Here's the downside of header wrap, the wrap elevates pipe temperatures, promoting cracking, and traping moisture, greatly accelerating corrosion, especially if the bike is operated in hard weather where the pipes and wrap can get soaked down. Now this situation can be delayed by wrapping pipes that have been coated with either high temp enamel or whatever ceramic coating you wish to use. HOWEVER, the wrap will STILL trap moisture next to the pipes and this can cause a quicker degradation of whatever coating is on the exhaust, and believe me when I say, RUST WILL FIND A WAY! It needs no assistance! 

No exhaust company in the world will honor their warranty if you wrap their exhaust. Old school race teams would wrap their headers to keep engine bay temperatures down, helping to lower the temperature of air going into the intake,  however the headers being run at 200 mph for an extended period of time were toast due to the wrap trapping all that head. Ceramic coatings accomplish this much more efficiently and last longer than a wrap. 

Performance wise, any scavenging effects you might gain from wrap wont ever be really noticeable... Most Honda Shadows are cruisers, not race motors. So here's what I would recommend, get the pipes coated, or chromed.  It will greatly prolong the life of the exhaust not from "crystallization" so much as from corrosion. It's a smart investment to keep your exhaust looking good for years to come. =)