your hobbies is what keeps your sanity in a relationship. Its your "alone" time.
Agree with this. What happens when you sell the car that (if like mine) takes up a-lot of your time? you get bored... and then everything you do from now on, is "as a couple". Which as bad as it sounds, will more often then not be a compromise.
keep the car, if she can't understand the love you have for it and that it's your hobby, then maybe she's not best suited to you and time to move on before kids etc become involved.
But in saying that, don't hold onto the care in spite.... if your ready to, sell it and move with her! But let it be you, not an emotional guilt trip that makes the decision.