I don't own a Miele, so take this advice for what it's worth...
Generally speaking, an AC induction motor with bad brushes will be not be able to deliver its nameplate power rating. It may well be able to develop full design RPM with little or no load, but it won't be able to perform its design function when actually turning a load.
If you hear funny noises like whining or growling, it's probably not the brushes, it's more likely the motor bearings.
Unless the funny noises are the drum not getting up to speed as it should and you're used to hearing.
Some motors with more open frame structures will demonstrate bad brushes by visible blue sparks/glow, but it seems unlikely that you could get that kind of visual from the picture of the Miele motor you posted.