@ Demi
NPC Items - I think you should consider when such an upgrade will come and whether it will feel like a real upgrade or simply putting an otherwise unusued piece of equipment on a character because it's technically better. I find this the case with Valygar's armor (no real options for him and he gets a good effect and good ac, which he needs in vanilla) and Keldorn's armor (this is more of an effect of swimming in basically similar heavy armors with no real choice until a unique).
Arrow of Dispelling - It needs a decent save penalty. -2 to -4 should fit.
Potions - I disagree with people clamoring for dispelling on potions. Most of them have a significantly short duration that they shouldn't be dispelled or can be balanced by lowering duration (I'm thinking Freedom, Clarity, Absorption, Magic Resistance all need to have duration's looked at). For me it has to do with potions getting dispelled on PC's but rather the other way around. The AI needs it's potion effects.
The potion of Mirrored Eyes is an outlier as it is used only very circumstantially and could be reverted to having being dispelled simply because it protects against a very rarely used effect and is only a problem in one area of BG1. I mean if there was a Medusa lair or something that would be different, but as it is, those potions when you rarely get them are usually straight to the sell bag. It's not even worth using them against vampires (the only other thing you really encounter with gaze attacks). Another possibility beside that would have them protect from only one gaze attacks (if possible) thus keeping the protection, but again you would have a problem with the Mutamin encounter since he will still attempt to dispel regardless of what is actually on the PC's.