My DH wanted to get a convertible. I POJA'd and said I would be enthusiastic about it if it could seat 4 people (with out major squooshage).

If she doesn't want you to get an expensive car, I will be it is because:
1) She has a differnt use for the money in mind
2) You get an awesome car and she gets a plain one.

I would ask her what her concerns are.