Are you sure of that ? I farmed Devilsaur on the start of Classic, with lot of layers (3+), and the respawn was 10 to 11 minutes, constant time. That how we managed to get 3 spawn every 10-11 minutes.
In my mind, dynamic respawn is only for low-level stuff, but maybe I’m wrong ?
Yes, Black Lotus is really expensive, on my server it was 50g before Dire Maul, now I don’t know why, but it’s 80g … Others materiial like herbs, essence of life, and lot of thing have dropped in price, but not Black Lotus.
I like the thing that Black Lotus is a very rare ressource, because you’re happy when you get one 
. But i agree the respawn window is to much (from 1h to 1h30 from what my friend say … 30mn window it’s just to much). I think the high window is just to prevent people to farm them, because due to 30mn window you can’t predict the timer and someone else can gather it on other spawn before you road into the whole spawn point. Sure you can ask your guild mate to stay on ALL spawn points and wait all the time, but frankly no one will do that because it’s … to much time consuming for just 1 flask.