I've always heard excess washing in the winter actually helps cause rust instead of preventing it. I believe the idea was the high pressure water used by all car washes actually pushes salt and water into places that otherwise wouldn't have been affected. This spreads the salt into hard to reach areas that will rust out quicker.
I've always tried to wash my cars every 2-4 weeks in the winter, but honestly I'm not sure what is the correct thing to do.
My wife has washed her 2000 sunfire maybe 3-4 times total in the 8 years she's owed it... only rush is just below the gas door, which is probably caused by fuel spillage.
'06 Black Onyx Ion Redline with Comp Package
ZZP 3.1", 42#'s, ZZP dual pass, ZZP phenolic spacer, NGK 4644, ZZP 3" catted DP, ZZP canned tune