Personally if I ever used a Dremel tool on contacts I'd use a fiber brush instead of steel for the flying wire bits.

With that said, the fundamental reason a contact will need cleaning is to remove an insulative "something" that is preventing it to conduct properly.
Dust accumulates on contacts and burn leaving carbon. If the current flow is sufficient enough it burns a pit in the contact and leaves more carbon.

For the low current applications like turning on a lite etc not much pitting or carbon accumulation occurs so I just fold a clean scrap of copy paper about 4x into a stick, put some rubbing alcohol on it to clean the carbon off.

Filing and sanding should not be the standard default method of cleaning every problem point.
Nobody has said it is, but i wanted to make it known. Removing a bit of contact material is usually necessary on those harder contact higher current switches such as flipper and 120v bank reset solenoids but not on a smaller, softer player 3 lite contact.

I use a hard mini small file when a few swipes with a file is necessary. I've had occasional bad luck with flexstone and wet dry sandpaper.
The problem I have is I trace an issue to a particular switch or segment of circuit and think I am cleaning the switch. .. and it looks clean too. But bits of sand had come off the paper and is left in the contact so it still doesn't work and I chase my tail looking for trouble elsewhere.

I still use the wet dry sandpaper if I can't find my file - but only if the alcohol method fails to get good results. I stopped using flexstone though for those issues .