Since I drive on dirt roads daily it's pointless. I was it once in a while to get the dead bugs and dirt build-up off.
Wait! On a serious note. However often you choose to wash you car is your business and and your choice. However, too many people don't wash thier windows when they stop for gas and ignore their, exterior mirrors and exterior lights. Every times you fill up you should take the time to make sure your windows and mirrors are clean and all of your exterior lights and reflectors are clean. You need to wash your interior windows as required to keep them clean. If the finish on your car is dirty, I may not find it unpleasing but it's not going to kill me. Dirty interior windows, on the other hand, that look fine during the day, can be extremely difficult to see throught at sunrise, sunset and with at night with oncoming traffic. Same with exterior windows and mirrors. Exterior lights: headlights, running lights fog lights, turn signals, tail lights, brake lights, backup lights, side markers and all reflectors, and for the police (I've been stopped for a bulb out) your license plate lights. All need to be clean and functioning. It's not just your safety, it's my safety and anyone else's safety around you.
Does leaving my Prius outside while tropical storm Hanna blows by count? I don't wash it often but I vacuum it out regularly.
I have a black Prius and it looks sooo bad when it is dirty. I keep the car in the garage and wash it when it gets dirty. I'm bad!
I love washing this car! We have a 250m dirt (mud) driveway so I get the opportunity often. I also wash it during droughts, cause it almost always rains after I wash it. ;-)
North Island. NZ had its worst drought on record this past summer (Jan to May). This was followed by the wettest winter on record (for many locations) The south island hydro lakes are currently at about 10% of normal levels. Can't wait for this year's cyclone season... :-(
I have a Silver Prius. It also becomes a Grey Prius. With a matte pattern. Forever different. Seriously, why wash the outside? I do the inside about twice a year.
Eventually. We'll still be in deficit for a while though. The weather is just getting more extreme. The godwits arrived from Alaska this week, two weeks early for the third year in a row. That's a big change for a migration pattern. We live in interesting times.