I never clean my car! I don't refuel it either.... I have a fuel fairy who also looks after keeping the car clean ;)
I think he cleans it every 4 weeks or so, my car gets filthy as my son attends a Forest Kindergarten and in usually covered in mud when he comes home, not to mention all the sticks, stones, pine cones and leaves that accumulate in his footwell. His car seat only looks clean in this photo as it was brand new - the mud monkey hadn't sat in it yet!
I don't drive, so I don't have a car, & my husband only cleans his 'our' about 1 a year. The outside gets really dirty, due to the trees overhanging our driveway, & the birds flying over, but the window wipers help a bit! The inside isn't too bad though. but the boot is VERY bad, but that isn't seen from the outside, unless it's opened to put some of the bags of shopping into it.