If it ain't broke don't fix it.
Maintenance is different. I never replace cap and rotor on MBs as routine maintenance. I very seldom replace parts from a preventative stance. At 150k a virgin cap and rotor might be good maintenance, but so would a radiator and water pump; where do you stop. Radiator necks break off quite frequently somewhere above that mileage.
I would do a standard 30k service. The one thing you don't get when you do it yourself is a look-over by someone like myself. I can drive that car and walk around underneath it and pick out more in 15 minutes than an unfamiliar tech or DIYer could in a week (or maybe forever). This may be the most important part of good maintenance!