Posts like this make me smile...
I don't care if you're selling something or not. You've got a looooong way to go if you think you've stumbled upon a great SEO secret hear my friend. Dealers across the country have been doing this for some time now, at least the ones who understand search engine optimization. With that said, most smart SEOs don't go after search terms which have little (if any) monthly global searches. Did you even run "2012 subaru impreza philadelphia" through a keyword analyzer to see how many individuals are actually searching for this term before getting pumped about such a momentous accomplishment.
All jokes aside, you got the right idea...just fine tune your process a bit more.