That's a little on the 30 year ago deep south profiling side, but the essence of it is true. If you've never skimped on lunches or stayed home or clipped coupons for the grocery store so you could afford a new set of wheels or to get the flowbench time on a set of heads, you've missed part of the experience imo. Most of us get past the point where we have to do that eventually but it's a right of passage as a young gearhead. If you open up the garage of a great many middle class suburban homes you'll find cars with owners that have 2x what they are worth put into them and happy to have done so, most of them can tell tales of working 2nd jobs and late shifts and such to make spare money to dump into a car when they were a kid. It's sort of a thing. It is difficult to find where to draw the line, strictly speaking it's the same rules an insurance company would use to total a car, if repair = x% of resale, ditch the car. Much harder to pin down the emotional/desire part. It's just money anyway. If it takes $10K to make you happy with a car that's worth $5K and it really makes you happy, the doing, the creating, the having, then it's worth it. Regardless of the math.
I don't think it's any crazier than buying a $500 cell phone that's going to depreciate to nothing in two years really. Least the car will still be good for something. We do more monetarily worthwhile European stuff at work and make a good profit on the parts from some and entire cars for others. It's perfectly possible to make money with this sort of thing, but it't not happening with the vast majority of cars. Gotta be love. The financial pitfalls are pretty self evident but there are strategies for dealing with them, one of the best being, don't count your receipts. Count your enjoyment. I agree the OP probly isn't up for what it's really going to take, but there are tons of people with that very car that do what his needs and more and love every moment of it. It'd be a moral failure to myself to not point out both sides of it to someone asking for advice. I think it's selling the issue short to call it a turd and say it's not worth it without exploring the hows and whys and facets.
I help people blow ungodly amounts of money on old cars all over the world, been at it seven years now and no sign of it slowing down, just the clientele has changed a bit as the cars have risen in value. It's all the same deal though other than the really high end stuff which is it's own interesting little world.