I can almost guarantee if two equally optioned cars in the same condition restored to stock, as built spec go across the block, the one with the HIP paint will bring more money.
This may be the case for A&E bodies. I also agree that it's even more likely for 70s cars vs 60s.
But one thing I'm sure of. Mopars have superior body lines that supports a wider range of colors. Even loud blustery colors. Case in point. Plum Crazy Purple. Can look baddass on a Mopar. But I once saw a Chevelle painted that color. And it looked like the definition of sadness. Lol. Really upsetting the Chevy guys. "Why is it painted Purple?" The reason it didnt work? I believe Chevelle doesn't have the defined lines and body layout to support bolder color options.