I'd go with an abrasion/polishing process rather than chemical. You can start with an appropriate grit Scotchbrite pad, then work your way to finer grits, then finish with polishing compounds on a rag, working from white diamond to tripoli or rouge, depending on the finish your looking for.

Note, however that these rims were never polished when new. New Nisi rims had what is is often called a mill finish, or the satin gray color of evenly oxidized aluminum that you might see on industrial or raw aluminum products. They used to weather to a duller gray, but like other bare aluminum items were subject to those white dots if left in a damp place for a long time.