Horred already dropped the XP of each creature you meet. This was to slow down the fast pace players were advancing. He also reduced the XP for learning spells and removing traps. Play BGT without BP (you can advance to level 4 before going into the Nashkel mines just by removing all the traps and locks around Beregost. So the BP game is adjusted better than a normal SOA game.
I have used a few forcespell scripts for my enemies and I am not always thrilled with the idea of the enemy "cheating" like that. No level 7 wizard should be able to cast 5 sets of magic missles. Same with some of the tactics scripts. Why can't I get my gnome to move that fast or hit every time he swings a staff? It is unrealistic.
I'm aware of horred already having changed the XP of many creatures, but tht balance seems to get disturbed again as new content is added. Wouldn't it be simpler to increase XP/level rather than having to reduce all the xp of enemies again? Maybe as an optional component for those who want a harder game still.