Restoring cars

I went to a classic car show where there were cars from 1940s to 1980s. Some of the cars had their engines replaced with engines from newer cars. Some cars have new brake systems, air conditioning, power windows, seat belts, etc. Some people like Jay Leno restore cars to brand new condition as if they came from the factory. Which is worth more money? Cars restored to brand new condition as if they came from the factory or cars "restored" with parts from newer cars?

Very subjective question, with a lot of variables, "restomods" have become popular, I have one myself, a completely modernized but stock looking 51 Chevy Belair. What I have done increased its value considerably. Do this to some cars like a true classic and it would be devaluated.