I guess it depends on the personality of the car.  Maybe it is heartbroken that people feel the need to change it from its original state- betrayed that it isn't valued for what's on the inside.  Maybe its afraid of the paint job, it hasn't had one since it was born, and it could be painful.

I have an old Mustang convertible on which I'm about to put a new paint job. It has a new top, but there are several imperfections and flaked paint which makes it look uncared for. With a slight bit of body work and new paint (less than $500), it will look almost new on the outside. It will give me more pride in driving it; it will draw a few stares from other motorists; and it will boost the value of the car.  

Perhaps it would gain a new lease on life- you often hear of people feeling more confident or having better self-esteem after cosmetic surgery or getting  in shape. If I had to write from the point of view of a car, that's what I would write about, though, as the first response observes, the process wouldn't necessarily be pain-free. Or, perhaps the new paintjob would make the car self-conscious, so worried about getting nicks and scratches that it was afraid to take the roads.

I would think an old car would feel a little relieved, because the new paint job would feel good.  I imagine it sort of like having old, flaky, wrinkly skin and getting new skin.  However, the process would also be a bit scary.  Cars often have to be sanded down, rust spots removed, and dings banged out.  This would be scary for a car because it may not know what is going on.