I dunno, I always disliked black wheels and think the silver looks just fine. To me, the contrast brings the eye down the side of the car to ground level and forces you to take in the whole car.

With black, it would be as if the car disappears into the backround.

If you're still sold on black, another idea for you would be to leave the trim rind area silver, giving a sort of whitewall effect.

As for paints, I have had very lasting results using Duplicolor Trim Paint (satin black) on the plastic (gray) underdoor trim on a 245 I did for resale. Couldn't get the wax out of the grain, so, I just repainted the thing. The black looked better than the original gray in this case, a cream yellow wagon.
--
1989 740Ti 1986 240DL 1984 244GL