Lack of time and a mending arm have meant that I haven't found/made the time to clean my Passat for just over 8 weeks, but due to going away this weekend, I thought I ought to make it look at least presentable. It was absolutely hanging, however I was amazed at how just a quick wash got it looking its best again. There had been two big bird poos on the roof for nearly 6 weeks. They just washed off without leaving any etching. Also the lower sides were completely free from tar spots.
The car has absolutely no protection on it. It just gets washed by doing a pressure pre-wash, AG shampoo used as snow foam, second pressure wash rinse, 2BM AG shampoo, third pressure wash rinse, followed by an open hose rinse off.
I reckon if you can stand it, leaving your car to get and stay dirty over the winter, is much better than constantly cleaning it and running the risk of inflicting swirls. Minimal contact and all that. The dirt seems to do a pretty good job to looking after the paint.