wrapping the header will def benefit if you wrap it right. It will keep and make the heat go where it's suppose to... out the back. A header as you know produces a better scavagging effect anyway so you are already flowing exhaust much better. So it does benefit. And having it wrapped will keep temps down def. If you have a race header it will keep the oil temps down. I'm going to wrap my hfc in a couple days myself... that will keep the oil temps down too and look better. it will also protect it mroe cuz the cat is just open to the elements wide open under the oil pan.
the only thing I can think of a header wrap will probably damage is the "shine" finish, probably after some years of use... other than that all the other things it does are good things!
*yes its an OBX header, people say they are cheap, but most of them havent even seen one! My bro didnt dyno this, but it sure feel a lot better, revs super fast, and def has more torque and power! To my surprise the header had a perfect finish, coating and welds. If you ask me, not a bad $130ish investment!
I got all the wrap parts at autozone
*sounds like crap because it has no cat ----stock mid pipe and muffler ---- replaced lunch box with a small fart can