Mike - You bring up an excellent point "clean them often and thoroughly". We bought a used 04 C240 Mercedes. The car was clean but like most Mercedes owners the wheels had been neglected. Took them off the car. Scrubbed the fronts and the backs and put a coat of polish on both sides and reinstalled them on the car. That was almost two years ago. They look new. I have a wheel brush that not only cleans the front of the wheel but more importantly the back of the wheel as well. That is where a lot of dirt and dust build up that ultimately finds its way to the front of the wheel. My wife drives several hundred miles a week and very little brake dust shows up on her rims. Most 240's I see the front rims are usually black, caked with brake dust. I clean the car weekly and the rims get polished monthly when the car gets polished. I guess the old saying "an ounce of prevention is worth a pound of cure" applies here. You can dump all the wheel cleaners you want on your wheels every month, 6 months whatever but if you don't maintain them with the same care as your car you are gonna have problems. A messy wheel and wheel well can really detract from the beauty of your car.