I have found that brushing is not enough and that seude shoes need cleaning from time to time.
Shoes are exposed to an incredible amount of dust and dirt by reason of tramping on dirty city streets and dusty country trails. Even in a "clean house" there will be a good amount of dust on the floor. Just go down on the floor, and see for yourself!
I have found that my brown and black suedes have taken-on a grey hue. A cleaning at the shoemaker has freshened the appearance and has taken away the grey hue. Generally, a cleaning will both highlight and darken the color.