I finished wet-sanding the rest of the ridges and scratches out of the surface of the throttle body over the past couple days here.  Ended up taking it to #800 wet for the finish pass, then polished it with mag-aluminum polish.  I'll probably go back and use a cutting compound first because there's still a slight haze on it, but it came out pretty good I think.  Well, good enough to make it hard to justify spending any more time on it.

Before:

After: