I think it's a good comparison!
Twilight and a PT Cruiser?
I loved that picture at first, but then I saw that.
Seriously, that is up there with my least favorite cars, if you like it fine, but I find it mind numbingly boring. Twilight is too powerful, reliable, and fun to be a PT Cruiser.
She would be, something that's powerful and fun, but not necessarily exciting.
Maybe the Audi R8, I remember Clarkson saying something about it being powerful and fun, but it was too refined and didn't feel very exciting, or dangerous. Coincidently his review of the ZR1 in the same episode made me think of Rainbow Dash, but the Mustang works just as well for her.
Other than that most of those are actually pretty much dead on to what I would have chosen.