Regarding the Gnoll's fortress I managed to clear it in two ways: with a huge use of sleep spells, or with Minsc with dexterity gauntlets and ankheg plate mail (both items available before the gnoll spawns). What are the exact difficulties your players have?
Also, I don't think there are more spawns than in vanilla BGT, but the spawns have a lot more creatures. I also didn't have the same spawn activate twice while in the area, so I think the timers are regular ones (or, if modified, not modified to spawn that often).
That said, I think BGSpawn is a difficulty enhancing mod, suggested for who's ready to retreat and rethink their strategies - since I've started using it, I had to revise my whole strategy method.
Just some thoughts to try and lend a hand. I'm sure mm75 will provide you more detailed infos.
EDIT: as expected, mm75 answered even before me! Mmhh spawns every 8 hours? I didn't notice that - with BGspawns and SCS1 I don't even dare to rest in wild areas.
Edited by kthxbye, 20 May 2009 - 12:01 AM.