When I bought my Sportster it already had 11 years with of grime and what not that had worked it's way into the pouris areas as well as the semi polished flats.
I bought an extra set of wheels, rear rotor and took them in hte be bead blasted and mirror polished.
When I picked them one the guy asked me if I was going to paint them or what the plan was. I told him I figured I could just keep them clean.
He told me the polished flats and the rotor/pulley would be a problem the the rought satin areas would just suck the grime again.
So after many hours of washing off polishing paste residue, degreasing and what not I painted mine using Dulicolor Wheel Primer, Paint and Clear.
Karsten