The annual service is the only time my car gets washed!
I have a "similar" approach to
outer cleanliness - on the inside, I'm quite a neat freak!
As I'm living in eastern Switzerland with quite heavily salted roads during winter, I frequently "Kärcher" the underbelly of my car(s) to get rid of the salt - you have yet to show me a car that started to rust through on the roof ("Lancia Sud" officially excluded!).
As for regular car washes: I was
complimented on my previous car's paint coat condition (after six years of similar "negligence") - so, go figure.