I had another '86 Mustang GT back when I was 21. I drove it for about 6 months, then realized there was no way I was going to be able to make it through an upstate NY winter with it. I sold it, and always regretted it, until I found my current '86 GT, which is nearly identical, except for the air and cruise that this one has. The one I have now is in even better shape, so really, I guess I don't regret selling the first one because it led me to the second one.
I've always been on the fence about my '93 Cobra. I had it for about 6 months before someone hit it in a parking lot. It was pretty messed up and I was really upset about it. I was in the Air Force at the time and the security policeman that wrote up the report ended up buying it from me after it was fixed. I broke even on it, and at the time, it was costing me a lot to drive and insure, but thinking back, it would have been nice to keep that as well. They just hold their value so well. Mine had 40K miles on it and was all stock. I was too broke to even do any mods:
http://www.wease.net/pics/Cobra1.jpg