You realize salt is inactive until its wet. If the conditions are dry and you have a layer of salt dust on your car, it will be fine. The moment it gets wet...that when the corrosive agents get going. I nice winter wax will help create a barrier between salt and metal and water will sheet it right off.
Really cold, dry days, I dont bother washing the car...its the milder slushy days that do the damage. :(
I just washed mine and the salt came off pretty easily...touchless in the winter