Really? There are no real mechanics or level design at work (which you can clearly see with Gridania being several times harder than any other zone out of sheer happenstance). It is mostly luck based when you get to narrow areas with both sound+sight monsters (especially when you have to pass several of them back to back, meaning any chance of survival is based on several monsters randomly roaming to the right spots at the same time). I don't see it. (I admit I had some fun through the sheer tension of it, but some spots were clearly designed not to be trespassed at all.)
Perhaps. It would be very cheap though. I don't think boss fights need to be as clever as the one in raids. Just make them tough (require tank, healer, and can take a beating) and give them one little gimmick ("one of its AoE special attacks silences instead of usual"). I would also give them a rage timer if they are not tied to some kind of timer otherwise and maybe a universal "draw-in".