I'm not an instructor, but am a participant and have been since BA 47. Put it this way, the only time I don't go is if I am out of the country on holiday, or for 3 months when I damaged both knees running (NOT BA - i hasten to add!).
I am not bored and neither are the full classes that I attend, yeah occassionally there is a bad track which does seem repetitive from previous realeases but its only for 3 months and my instructors usually mix the lesser ones out and replace with our suggestions.
For me and my friends who attend, it is the workout - lets improve and actually do it harder and better, the music - the more inspirational the better, I like to sing along (helps/makes me breath), the instructor - if they are positive and "up for it" and not dissing a track, song or move - then, quite frankly it will go un-noticed that its not that fab.
However, i have also done BA where the instructor (not at my normal gym I hasten to add!) has behaved as if they don't really want to be there, introduced each track as a lower option and been quite open that they don't normally teach this/like the music etc........................needless to say I did not go back!
I love BA and qute frankly if the instructor dosn't want to teach it - then don't. I'm sure theres a nice legs, bums and tums class out there that needs an instructor.

Attack addict!