rattle can vs. real paint
OK, first off, the real not so secret secret to a good paint job is doing the prep work correctly. If you don't do that correctly, it won't matter what kind or type of paint you use.
Secondly, someone mentioned that their van required about 50 spray cans. Let's just say it is three bucks per can, cause after all, you want the good stuff. That's $150. You can buy a quart or two of Dupont Nason for less than that.
Unless you are simply trying to waste your time, I wouldn't bother with spray can for painting a car. The exception to that is for some of the very specific products that Eastwood and others sell in rattle cans.
My two cents worth,
Dennis W. Parks
author of automotive how-to books