Robert, are you looking to get out of the project or just commenting on the financial formula? If you are looking to move it along, parting is another option that might actually net you more in the end although it is always too bad when a restorable car is parted out. No worse, I suppose than seeing it street rodded though. People who need the stuff get it and that is a help.
If the comment is that the dollars won't come back, that is true, but the worst point in terms of return is when you are mid way through the project.
I like Tom's approach in post #6. I think having a plan for each car helps. In our case, we have 3, that is enough to do what I want to do without overwhelming from a time or finances perspective. One is maintained and enjoyed with a goal of keeping all original. The other two are early Fords - handling the A roadster as suggested in post 6, aging cosmetics stay for now, when decent mechanicals are 110%, will look into a pro cosmetic restoration on that one while I am still working and can afford it. The last, T speedster is for me to restore as much as possible by myself. Financially, the most likely winner will be the first car, a sports car with a rising value right now although care and feeding adds up over the years. The A is likely break even now, with a planned over-investment in the cosmetics and the T is likely a small loss now, which won't get better when finished, as you say the nature of it. Very few hobbies pay off financially - or they would not be hobbies I guess.
Anyway, good luck with it - I guess the point of my story is as long as any losses are not life changing getting too hung up on values is energy spent that could be spent enjoying the cars one way or another.
Good luck with whatever you decide to do with your tudor!