What's you point of view about BWP ?
Well, I played the vanilla CA when it was still being developed, and you can see actually that part of the old enhancements are part of the mod, things like the thac0 & other tweaks(new spells, AI enhancements, NPC exclusive kits, added items +more), as the CA itself is based on one of the old BP builds, which was the ancient version&inspiration of the BWP/S. Some of the AI features over the base vanilla BG2 are harder hard to tell most of the time, as the story's encounters are build for the ruleset in the game, and the placement of the enemy are well set.
The balance is build on those bases and if you tweak the values too much, you might get non intended off balance. Which side depends on the exact tweaks. Aka if you install OP spell mod, you can "easily" kill the opponents with those spells so that you won't even ever see one of them, but that's cause you installed the OP spell mod.
Some of the vanilla's fixes were also included, but as most fixes are kinda story dependent, so they are not needed. Things like alignment changes (that effect spell selection etc), item usability (not needed as they are not present, example being an NPC's full plate armor that was usable by a monk, not being present in the game as the NPC is not there to be recruited).
I try to support the BWS's approach to installing mods to the BG2 game. That said, as a Total Conversion mod, the mod doesn't really need any other mods. Of course if you wish to install any rule change mods .. it works there to a few limits.
Yep, Jarno Mikkola. my Mega Mod FAQ. Use of the BWS, and how to use it(scroll down that post a bit).
OK, desert dweller, welcome to the sanity, you are free to search for the limit, it's out there, we drew it in the sand. Ouh, actually it was still snow then.. but anyways.