I don't know. mupen64plus is pretty good for playing games, but AFAIK, none of the N64 emulators are where bsnes/higan is for the SNES right now. There's apparently an N64 emulator that's trying to become that accurate. It's called CEN64. I've never used it. From perusing the web, it sounds like the system requirements are pretty high.
You know, the N64 itself may be the best option for testing N64 homebrew, hacks, and such. You can get one of those SD card cart things. They're crazy expensive, though.