Well, you can wash it too often if you are using too harsh of a soap.

I rinse mine with warm water and a cloth EVERYTIME I drive her - just the nose, mirrors and windshield trim - this is to get the bug guts off before they dry on.

I think wash it by hand about every week - depending on how much I drive it. I don't use car washes, they tend to get the top wet (and I don't like it getting wet OR getting direct sunlight any more often than nessesary) and I don't trust car wash soaps.