There are two kinds of people who own cars, people who keep their car clean and tidy and well polished, and the people who dont care. It's an interesting phenomenon, when you consider how much a car costs, both to buy and then to keep running.
Regardless which type of person you are, there are some reasons to keep your car clean that you may not know about.
The first is the most obvious, cars that are kept cleaner last longer and perform better. This is because cleaning your car, at least the outside, removes the salt and dirt that can damage not just the exterior of your car, but up inside the engine compartment as well. Consider for a moment what happens when you drive though a puddle, especially one that has both mud and salt in it from winter driving conditions. The salt and mud get splashed everywhere, including the underside of your radiator, the underside of your oil sump, inside your wheel drums and in some cases even up into the coverings of your engine itself. And you probably don't have to be told this, but salt is corrosive. It causes metal to rust and rubber to decay. This means holes in your silencer or exhaust pipe, oil sump and radiator if it's not regularly cleaned off, leaks in your oil pan gasket and deterioration of your brake pads, shoes and linings.
Regular cleaning of the exterior of your car also helps to preserve the paint that is applied which means less rusting and color that fades less quickly.
Also, there is a link between the cleanliness inside your car and how well it is maintained over all. It has been shown that those people that keep the inside clean also tend to take the car to have the oil changed when it's needed, the tyres properly inflated and keep those maintenance appointments.