I've been struggling with this exact question for the last year or so... With values where they are, even a beater BB/Manual Chevelle like mine would bring $20k without breaking a sweat... but my car still needs body & paint for me to be truly happy with it (and suspension, and misc other upgrades).. at least another $10-15k and likely more 10 years at my present timeline... at the same time my "usage" desires starting to not match up(really want to take it on some long-ish road trips). It will continue to eat my money and time in the pursuit of those goals...
The transmission going out this past sept may have been the death rattle for my ownership tenure... I'll have it fixed and on the road again soon, but thinking very hard about selling it this spring/summer when the sun comes out again and buying a 2015+ Mustang GT or Challenger or Camaro to replace it.
I may also pickup another 47-54 Chevy Truck to have something old to dink around with since they are still extremely cheap and easy to build- but the draw of having something nice, powerful, AND reliable to play with is becoming hard to ignore.