IMO . . . (with all respect) . . . I would say the surface chemical conversion of the special primer is better. But then, I think Mag wheels should be expendable and thrown away after there life expectancy. However given there now rarity, they need to be keep servicable as long as possible, Pushing 50 year old wheels another possible 20 with an expensive process versus powder coating is yet to be determined.
I think this point has my restorer (GunnerZ) in stand off with me. (Haven't communicated with me since)
Now as for touch up . . . a powder coater told me they can spot heat and flow plastic over a damaged area, easier than painting.
Before I toss the Campies, I might give and let them blast and powder