Is that to give it a better finish or just to give extra protection.
My powder coated Raleigh doesnt look brilliant, a little flat perhaps..but despite circa 4 years of all winter commuting, the coat is as good as the day it was applied.
If its purely extra protection, its not neccessary IMO. That said, if its applied by aerosol, it wouldnt cost that much anyway as a DIY thing.