Did you ever consider just keeping the cars, and PUTTING YOUR PS3 AWAY FOR A MONTH...?
Seems like an insane answer to a problem. To get all those cars, you have basically been locked in a room for weeks! I can understand her getting furious, but unless you lose the PS3 permanently, it's not a solution. They have all kinds of twelve step programs, and I'm sure there's one for gamers who ruin their personal lives for a GAME!
Just treat it like any addiction. Come off it cold turkey for a while, then allow yourself x amount of hours a week, AND STICK TO IT.
She'll love you, you'll have a life, and some nice cars to drive when you DO play (for just a few minutes!)