I just bought a 1987 Centurion with what appears to be the original components. Even after washing, the anodized parts seemed a little dull/stained, so I tried cleaning up a couple of spots on a brake caliper and one of the rims with a soft cloth and a little bit of mild automotive paint polish (not even metal polish). After rubbing the spots lightly, they cleaned up nice and shiny, and there was black residue on the cloth that I'm assuming is aluminum oxide.

I've read elsewhere that anodizing degrades with time and has a useful life of 10-20 years, although that number wasn't in the specific context of bike parts. Does it sound like the anodizing is gone (or nearly gone) from my parts? I didn't want to go the "strip and polish" route originally, but if the anodizing is almost gone anyway I don't have a problem with hitting the parts with some Simichrome or Flitz to get them pretty again.