I would still expect better protection from a vinyl film than a spray, due to the difference in thickness and composition though.

 

We had a 3m vinyl clear bra on one of our cars. It worked pretty well but after some years, became impossible to remove and developed a cracked texture. This was more than five years after the application on a car with normal use. So, these aren't a consideration if you'll be selling the car on a few years after you buy it but could be for the longer term.

 

While you are at it....3M pro film by the roll http://www.amazon.com/s/ref=nb_sb_ss...rotection+film

The "pro" series is a better film, does not yellow and supposedly is easier to remove. You need to have a nice coating of wax on the the paint before you apply any film as they all can get backed on. Once backed on, you have to use a glue remover to get the film off. You are also correct that spray on will not perform as well as film itself.

If you notice most 911 Porsches will have some clear film over the rear fender sides. The product works, but you should remove and reapply in a few years.