I used to be anal-retentive about washing the car every weekend, waxing often, etc. Nowadays I clean the cars when they look grungy, but do small touch-ups on certain parts in between. Interiors are never filthy or grimy, just usually sandy and dusty. I'll wash the wheels more often than the paint.
That said, I definitely need to give my cars a thorough detailing just to make sure they stay looking sharp.
I think this guy is in the "dirty, drive it" camp...
(Keanu Reeves)