I have a stock can that has had no less than 5 arms through it. In regular club racing I run the brushes till the serrations are gone, sometimes longer, then I may drill a hole in the brush. I never race discolored brushes, and my car is always decently competitive in the speed department. Once in a big while I will turn the motor in to get it re-tuned with the equipment I don't have (magnet zapper), and this particular motor always bounces back fairly close to it's original performance. It's a myth that you have to re-tune a motor every run if you want to be fast. I witnessed first hand a team driver that left his motor in his car for every race run at the IIC, and his car was ballistic every round.
I will, however, agree that for now brushless motors will be more economical for the average joe club racer that heralds to the current creedo that you have to re-brush every round and the motor should be thrown away after 40 runs. But I am of the opinion that these racers are either made of money, or don't want to learn the very basics of keeping a motor in tune (which is not hard work), and are dying to drop some serious coin on the newest gear.
I am waiting for the day that people are complaining that they have to hire someone to re-tune their speed controllers because they don't know how to code, or forgot their PC at home.