I would be more worried about the wrap holding moisture against the pipe and leading to corrosion issues. I guess it would dry pretty quickly when riding, but if you wash it or something like that then it could stay wet for a while and even stainless steel corrodes.
I don't think high engine temps necessarily shorten the life of the engine, since it is designed to operate at a certain temperature. I would like to think that Yamaha engineers did some flow calcs when designing the cooling system and the single rad is probably more than sufficient. When riding at any speed, there is probably very little convection between the exhaust and the radiator as air flows over both and carries the heat rearwards. I could see sitting in traffic on a hot highway causing more heat issues.
You could also run some Engine Ice coolant which runs a bit cooler than the standard water/anti-freeze mix if you are concerned.
But if the wrap is more piece of mind, and keeps your right leg cooler and your pants from melting, then it sounds like you did it right. Post up some pictures; we all love pictures...