if the majority of illegal downloads really were just "curiosity/see what it sounds like" downloads, the record industry quite simply wouldn't have noticed. It wouldn't have even registered as a blip. Instead, it's taken a massive hit.

Is the record industry going to take a massive hit from downloads of old Leader/Trailer albums?

You're arguing against huge numbers of people downloading commercially available material. I'm arguing in favour of small numbers of people (e.g. the population of Mudcat) downloading unavailable material - and I think that's pretty much what SO'P is advocating, too.