I've noticed that Saturn games have gone up in price lately. And as for younger people not knowing about Sega at all, I don't think that's true. Kids of my generation knew about the Genesis, though the SNES was probably more popular. Just because the SNES was more popular doesn't mean there weren't Sega fans.
Yeah, im 15 now but ever since when i was 7 or 8 ive always tried to find infomation about old unheard of consoles. For example, I would ask my parents, when all the kids wanted a xbox 360, if I could buy a genesis.
Let us not forget that Sonic is still a huge franchise despite many of the older fans giving up hope. As long as Sega keep milking him for every penny the newer fans will always back peddle to the Mega Drive era in search of his origins. That alone should keep some interest in old Sega consoles. As for systems such as the PC Engine and Neo Geo, they will always rely on the hardcore fans to keep them alive, eventually one day demand for them might cease altogether.