When deciding how/when to wash your car, you've also gotta consider your conditions, too. Is your car parked outside all day every day? Mine is. Do you barely drive it? I've got 36k miles on my MSP so far in around a year's time. Are there factories around you? Yup. Construction? Yup. Stupid immature kids that egg or throw coke on your car? Yup.
I clay my car so often because I feel it needs it. "Normal" people may not need it so often. However, since I smoke, it's pretty easy for me to get the plastic cellophane, put my fingers in it and run it over the car every time I wash it. You can notice a *LOT* of imperfections that way and I don't like that. Clay bars remove most of those and then the cleaning polish after that removes even more.
Mequiar's has an "Your Car's RX" or something on their website. I'd recommend that people go check it out. It's basically a form you fill out with your location, driving habits, parking locations, etc. and it suggests a washing routine. I'm not saying it should be your standard to follow every time but it helps get an idea of what you should be doing.
Also, for what it's worth, do NOT wash or wax your car in circles. Use a back and forth motion, even with soap and a mitt. This is even more important with cleaner and wax to prevent swirl marks. I guarantee you will not find a single swirl mark on my car, even with it's frequent washing.
NXT is also the easiest wax I've ever applied & removed. It may not last longer than 3-4 weeks but that's not a factor for me. I'm not about to spend >$100 on wax again, period. Zainos is far overrated in my opinion now that I've used NXT.