As far as the older systems go, it's too difficult to find them or the games anymore. If you think about it, the companies aren't even really making money off of them anymore. They just circulate around the general populous. They might still be making money off of the franchises but the games themselves, like super mario bros, aren't making them as much as they used to.
I see no harm in using emulators. I've got roms for Legend of the Dragoons that I play sometimes on a PS1 emulator but I also have the original disc set and a digital copy on the ps3.
You should totally try and play super mario 64. That game is a total classic