If you don't need the cash right now, holding onto it may be a good thing. You can avoid being the guy that we ALL see at car shows that says...."I wish that I had kept that car".
Cash isn't an issue in the sense of, "If I don't sell the car I'm going to be broke." Right now, space isn't one, but can be in the future. I'm working on getting some space at my current home so I don't have to drive 20 miles in SoCal traffic just to see the Dart. If I'm able to obtain that space, and bring the car here, then I'd be more motivated to work on the car more than I do now and keep it up.
But, my priorities with the car have changed since I first built it and I think I want to change the car up drastically. However, I just want to put my time, money, and energy into other things right now and come back to the Dart later with my new ideas. I'm just focusing on my family, career, and happiness.