Higher difficulties spawn more enemies in BG1, and have been since the original release in 1998. However, higher difficulties don't spawn more types of enemies or improve enemy AI like they do in SoD.
In BG1, difficulty also only affects randomized spawn points, not static enemies. So you might find more gibberlings by the side of the road in a wilderness area, but you won't find more bandits in the Bandit Camp.
Comments
Making the game more difficult without increasing enemy damage is the way forward.
Pack the Bandit Camp with Assassins using poison weapon and/or back stab, more Kobold Commandos in Nashkell Mines, stuff like that.
I guess we have SCS
If difficulty works similar without SoD now, higher difficulty apparently would mean more and stronger enemies.
In BG1, difficulty also only affects randomized spawn points, not static enemies. So you might find more gibberlings by the side of the road in a wilderness area, but you won't find more bandits in the Bandit Camp.
So, it's indeed interesting to know if there're differencies between Core Rules and Insane with the no damage increase option.