The idea is that once you have an accurate emulator, everything just “works”. With an inaccurate emulator, the developer has to make hacks and modifications for nearly every single game. This means that it’s possible for rom hacks that have been tested on that inaccurate emulator to only work IN that inaccurate emulator. That is extremely important because then said rom hacks would not even run on a real SNES, let alone any other emulator (note that this HAS in fact happened already).
And besides, that “3ghz CPU” requirement isn’t exactly true anymore – that was 3GHz with a Core 2 Duo or Athlon 64. If you’ve been paying attention, you’d know that modern CPUs are 50% to 100% faster than those older ones, making the requirement only 2GHz or lower. This is something even a mainstream laptop can achieve nowadays.
But what about the cartridges? Some of them have special chips such as Starfox with its FX chip.
I think a better thing to strive for than perfect emulation is perfect user experience. Save states, which don’t exist on the actual hardware, creates a better user experience. They are so good that even Nintendo adopted them.