In my opinion, it is worth having a cycle accurate emulator or two per system. The inevitable research that comes from creating them, such as weird edge cases that only affect a couple of games, filters into the more optimised emulators that most people will actually use. I don't use bsnes personally as I find it to be too slow, power hungry, and lacking in useful features for casual use, but I do follow its development with interest. I've seen how certain findings from bsnes have filtered into Snes9x.
Cycle accuracy does have great benefits, but does that mean we should dump our current emulators on our hard drives for totally cycle accurate ones? Should all current emu devs all move to cycle accuracy alone? I think not. I think more and more people are running emulators on netbooks, tablets and consoles etc., so portability and optimisation is important as well. But without the research that comes from 'accurate' emulators, these faster optimised emulators will have lower compatibility since updating them becomes prohibitively difficult and time consuming.
The Snes was pretty accurately emulated before byuu started his emulator, so the overall gains from his research seem pretty niche to the casual observer. However, current N64 emulation is still riddled with often game breaking bugs and has game specific hacks for pretty much everything akin to uosnes. Even the more popular titles, like Donkey Kong 64 and Banjo-Tooie have game-breaking core issues. As a fan of the system who has played about 40 of the most popular games on the real hardware, I can say with conviction that the current emulation is currently not there (even if you have all of the current best plugins and emulators, which I do have). z64 made good progress to alleviate some of the issues, but it can't solve all the problems inherent to the emulators that are currently doing the rounds.
So, research from creating a cycle accurate emulator with an excellent debugger would mean more research for the faster emulators (which are now all open source, so the means is there). Then we can all run more accurate fast emulators on our netbooks and tablets and not worry about battery life.