Good luck on the decision process. I struggled with the "do I sell" question last year -- had a Bugeye Sprite that I had put a lot of time and effort into and never intended to sell. Long story short I acquired my MGB and found myself contemplating selling the Bugeye after all. Took me all summer to really think it through, and in the end I sold it on to a BCF member. I've not regretted the decision, though I struggled with it.
If the car is no longer something you enjoy having around, then it's time to sell. No sale can take away your memories of working on it with your dad.
Tough process, good luck.