I've always been a big believer in backwards compatibility but I honestly don't remember it being a big deal with the NES vs. SNES. And to be fair, I'm not sure it would have been something that would have been economical, especially given the tendency to upgrade NES games with additional hardware.

There was also a cheap converter for the Game Gear that allowed it to play Master System games (it was basically a portable Master System anyway) though I don't recall if that was a Sega product or not.

Given how popular the Genesis was, backwards compatibility on the Saturn could have been the killer app they desperately needed though.