i'd clean it really well with mean green (or your cleaning product of choice), then give it a bath in evaporust to get the rust off...

you could also give it a short bath in clr to clean it/get certain crap off... but note the word "short", as clr may (will?) eat the finish off as well...

sure, you could send it out to be re-finished/re-plated... if it's rusted, there will be pitting, so the finish in those areas is gone...

all depends on how much money you want to spend...

Pull it out, run it through the dishwasher, wire brush off any remaining rust, spray paint it grey, put it back.

I just did this on my Star Trek: Mirror Universe project.
http://pinside.com/pinball/forum/topic/star-trek-mirror-universe-pinball/page/8#post-1525509

I used 80gritt sand paper to remove the gunk / rust (after disassembling) then powdercoated the bar. Reassembled with stainless steel hardware.

I chuck them in my vise and use a brass bristled brush in a hand drill, or use heavy leather gloves and put the brass brush in the drill press. Then, you'll want to refinish them in some way, as you've now stripped any of the original zinc coating that was on them off, and they will rust much easier now.

Most times, you're better off buying new if you want them to be really nice.

I just use a wire wheel to remove the gunk/rust. Now it does remove the finish, but I just shoot it with triple thick and call it a day. I like the clean metal look myself.