I used to wash my rides all the time, sometimes up to 3 times a week. With all the upkeep on the house, yard, work, hobbies, and wife, I find I don't have time to work on washing anymore. Now, as I've gotten older, I might wash them every month or up to 3-4 months.
However, every 6 months, I wash, claybar, compound (if needed), and layer on Collinite 476s topped with 845, polish the glass/lenses/lights, slap a layer of RainX on the windows, clean it out, etc.
I try to time these things for April/October, when it isn't too hot. March and November are usual maintenance months for me. It's nice to have a schedule.