There is a buffing kit for Dremel tools with polishing compound and a couples of different attachments like a cotton wheel and some others cotton tips.
Never did ball guides but was using it for detailing on small parts!

If you're looking to just clean up ball lines I've found they work well using the wire wheel attachments and save a lot of time over manually sanding. If you're trying to polish them to a mirror if finish, not so much. It will take you forever and you wil get very uneven results. You really need a buffing wheel and need to do it outside or in a garage at least as rouge gets everywhere.

Never try and buff a ramp withe a Dremel...

I've used a dremel with the polishing discs to polish ball guides. Wipe some mothers metal polish on it and polish away. It will take some time but comes out nice and shiny.

It won't work. You will ware out tip after tip after tip and get nowhere. You will ware out your dremal tool. I have tried it. If you want them polished buy a grinder with a polishing wheel. If you want them regrained buy a sandpaper flap wheel that will fit on a drill. Even with a polishing wheel on a drill you will spend hours, burn your fingers, bend your stainless pieces and more. I had a piece fly out of my hand and hit me right between the eyes cutting me from the base of my nose to underneath my eyebrows. If it would have hit me in the eye I would be blind in that eye. It isn't easy. Now I only polish the part that you will be able to see when the game is assembled.

Here's a nice tutorial by Terry on how to do this.

Re-Graining Ball Guides
http://pinballrehab.com/1-articles/pinball-restoration/playfield-parts/181-re-graining-ball-guides

Re-Graining Metal Ramps
http://pinballrehab.com/1-articles/pinball-restoration/ramps-and-plastics/182-re-graining-metal-ramps

Polishing Metal Scoops
http://pinballrehab.com/1-articles/pinball-restoration/playfield-parts/97-polishing-metal-scoops

Thanks,
Mike
www.HabosArcade.com