Originally Posted by BCRider

Wax on the braking surface is not something I would want to try either. At best your brakes will just be squeaky from it. At worst any silicones or other modern slippery stuff in the waxes will result in less friction and reduced stopping power.

And even if you did sand and shine up these sidewalls to a mirror like shine the shine would last until the first stop and they'll be all marked again.

The arched part of the rims is anodized. Using waxes on anodized surfaces will result in the whitish buildup staying in the nooks and valleys that make up the matt finish of the anodizing. It won't clean out and shine up like a painted surface would. Instead it'll remain white'ish.

Going beyond that would be removal of the anodizing and then polishing. That's a LOT of work and the bare aluminium will actually be more prone to corrosion and pitting from exposure unless you keep them waxed with a good automotive wax. But then you're back to the wax on the braking surfaces again.

Unless you managed to stain the anodizing with something I'd suggest just wash them well. If you've picked up some road tar stains then a mild degreasing solvent can be used to remove then and follow that with a wash to remove the solvent.

And finally power tools used around the rim are going to also hit the spokes and spoke nipples. An abrasive that is harsh enough to remove the anodizing will certainly result in the wrench flats on the nipples being worn down and then you risk the nipples rounding over when you try to true your wheel at some point.

Nope, I'd say this is a time to just wash when needed and step back from the compounds, waxes and power tools.

EDIT: I see you're trying this on a used rim first. Good idea. I still think it'll be more work than it's worth. You're going to get road and brake crud on it anyway. Especially if you rid in the rain at all. Actually when you ride in the rain MOST of the black stuff on the rims is brake pad and rim sidewall residue. Very little of it is actual mud picked up from the roadway.