...infamous for driving desirable cars (SS100s, DS23 Decapotable, Silver Ghost, 6.5 Bentley, etc etc) and not washing them (nor did he maintain them very well, something I don't agree with...)
Personally, I only wash the car when it really needs it. Bucket of water and some whatever car-wash is in the cupboard. Then a wipe down with a proper chamois...car usually lives under a soft cover, so it doesn't get that dusty.