There is no way on financial or logical terms that you can justify your old Volvo. However, there are plenty of emotional reasons:

1. Satisfaction of having rebuilt and restored an elegant machine yourself.
2. Satisfaction of knowing you can finish mechanical and practical tasks that very few people in our disposable US society can now do.
3. It is probably more fun to drive than a modern all-electronic car
4. If you have already invested heavily in it, why sell it at a major loss, especially, as you said yourself, you will only get a tiny fraction back?
5. Use it as a daily driver. I am convinced it is good to rotate car use in the household.
6. Anyone with money (or a desire to lease) can drive a new machine. There is nothing cool about that. Driving a 36-year old car is cool.
7. The day after you sell it, you will probably regret your decision.
8. Keeping an old Volvo running is relatively modest compared to what many hobbies cost (hunting, SCUBA, house-decorating, etc.).

Good luck, and I hope you keep it.