To me, they are works of art and reflect the personality of the owner and restorer. I can relate to both correct restoration or updated. Rarity and provenance of a particular vehicle do come to mind as considerations. There are genres that do nothing for me, but I can still respect the work done and attention given to them.
In today's world, I would have a tendency toward reliability, safety and consistent performance as benchmarks. Again, rarity/provenance taken into consideration. For example, I would rather have a modern, clean burn motor, better suspension, brakes and tires, but not on an original documented COPO Camaro.