I, too, am a dinosaur, and in my experience, we used primer to cover up bare metal and deter rust for a short while until the body work was done and the car could be painted proper like. Sometimes our finances were a deciding factor, as well, but nobody I knew in the fifties and onward left their car in primer as a finished item. Looking back even farther, many of the cars seen in photos from the thirties, forties and earl fifties were not in primer, their paint was dead; no amount of elbow wax would do much for it. In the thirties, the common mand had not the means to afford polish, nor the incentive to use it; a car was a tool, more than a toy, and it was kept reasonably clean and serviceable, but unless one was a large amount better off than average during the depression and just after prior to the war, shiny cars were not in the necessity column. My Dad had a '29 Model A roadster when I was born, and it was the apple of his eye - but it was not shiny black, only clean, and I can barely remember it before he sold it and bought a '38 Olds 4 door. It, too was dull, but it was blue, just not polished; polish was hard to come by for the most part in those days. He traded the Olds in on a '52 Buick, and it was the first shiny car he ever had, but it was only a year old. So, I think a lot of folks today look at old photos, and think they are seeing cars in primer, when in fact the cars were just a product of their time, and never saw a polish job.