I'm going to give you my real quick version of a painful story...
20 years ago when I was a young lad I bought a 90 Notch. The car was a pile. Built it up over a few years and made it exactly what I wanted. Granted I was young, engaged, had no huge bills when I built it. I spent a TON of time and effort on that car with friends and we had a blast. It wasn't too crazy, but it ran 11.8s on an NA306 with stock style suspension...
Fast forward a few years. Had a house and a young son who was just born. Still wasn't being beat up with bills. Both wife and I have always worked fulltime jobs and had great local family who helped with the young family. We weren't beat up for money. One day I decided that I wasn't driving the car much anymore, there were some little bills I could pay off, and I made a real bad mistake.
I sold the car. The day after Christmas, I dropped it off at the train station and on it's way it went. My good buddy also sold his at the same time because "we weren't driving them anymore." Neither of the cars owed us anything.
I don't regret many things and I'm not the type to harp on my past decisions. You make them, you deal with them, you move on. That's one decision I really regret. Once it was gone and the money went to the bills or wherever, it was still gone. Come to find out a few years later that it had been totalled by the person who bought it and it was scrapped. Gone.
It took over 15 years to get one back. I bought a 92 LX, spent some time with it, spent some good money on it, did the 351 swap I always wanted to do, and then sold it. I just never fell in love with it like I did with my notch. It always reminded me of that stupid decision I made. I used the money to help pay for the Cobra.
My Cobra? That's here to stay! That's never going anywhere. I LOVE this car. It puts me right back where I felt when I was wrenching on the car with the boys 20 years ago. I refuse to let this one get away. I made that mistake before and I absolutely refuse to do it again.
So think about it before you really make your decision. If you really feel the right thing to do is to sell it and move on, take another couple days and be sure. In the end, the decision you make has to be the right one for you. Just make sure you're doing it for the right reasons.
Good luck!
Man, this is almost my story exactly. I traded my 89GT in for my Roush. Had a chance to get my 89GT back, but new owner totaled it before I could buy it back.
My Roush is cool, but if I had to do it over again I would keep my 89GT. I put myself into that car. The Roush is cool, but it's someone else's vision. I have put myself into my 03 Cobra and I enjoy my Cobra more than my Roush.
Based on my experience I say keep the car. It's easy to say you can buy another one in 5-10 years, but you don't know what the quality will be or what the value will be.
Good luck in whatever direction you decide to go.