I have these same wheels on my E60, but three of them are in serious need of refinishing (do to my failed attempt at the "nasa method" to repair curb rash. I went so far as to eventually completely repaint the three bad ones with Wurth paint and clear coat, but the results I got ranged from "meh" on one wheel to OMG WTF did I just do?!
I took them to a wheel specialist and he suggested that I have them media blasted and powder coated, which I'm seriously considering.
Looks like you are happy with your results! Mind answering a few questions?
How does the finish compare to the factory original (especially smoothness)?
Did you have them media blasted first?
How long did it take?
How much did it cost?
Much appreciated!