And if you buy the Game Pak and a Kazzo or Retrode dumper, you have a defense under 17 USC 117(a)(1) (or foreign counterparts) if someone does sue you, so long as you can afford a lawyer and don't distribute the dumps.
Actually, no. That defense doesn't work because you're format-shifting. More specifically, you're going from a format that doesn't have copyright to one that does - you are not allowed to dump ROMs, period, without a legitimate developmental reason.
It's a funny thing, but a mask programmed ROM is actually not copyrighted. It's Mask-protected (it's a M in a circle, similar to how copyright is C in a circle). Mask works have higher protections, and even though you can easily dump it, the conversion from physical to software is actually completely illegal.
The one exception to that, is for developmental reasons - you're developing something that requires the data in the ROM. In which case you are allowed to have it only for that reason for the duration necessary. (Sony v. Bleem confirmed this when Bleem had Sony BIOS dumps of the PSX - it was determined that Bleem had the legal right to have those dumps, as they were necessary for the development of the Bleem emulator. But Bleem could not distribute those dumps, and must destroy them when complete).
It's one of the reasons why Nintendo kept cartridges around - there are plenty of legal protections for software embedded inside of a ROM (more generally, any IC) that aren't available on more traditionally available media.