They would also clean up the brush holder area which gets crapped up with carbon over time. The brushes need to be free to move against the commutator. You might try just doing some cleaning first. I am not sure if you can do this with the generator still in the car or not. It only involves taking the cover off the end. I can provide a photo as I have a spare generator.
If you do take it to a shop, take the Regulator with you and they can test them as a pair for you.