I'm pretty sure that crank was not anodized. The pitting you see is typical of the way aluminum weathers (oxidizes) when it has not been anodized. If you sand through an anodized finish, you can see it very clearly. The anodized surface has a slightly cloudy, satin kind of finish; more gray than silver. The bare aluminum is more highly reflective, so depending on the light conditions will appear darker or lighter (or both!) than the anodized finish.

So you don't need to strip anything. If you want a better finish, just keep going with wet sanding; I'd start with 320 grit, progress to 600, then maybe 1000; and finally polish with brasso or whatever you like to use.