I'm all in favour of nerfing mods. I certainly think there should be a much wider choice of what restrictions/changes one wants to implement. For example, I seriously object to any XP-nerfing even when playing a BWP mod as I'd like all my PCs to reach 30th level minimum by the end of the game(indeed, I use a modified cheat from a smaller mod which allows me to grant 2 extra xp points for every standard xp point gained, so that my characters can reach high levels despite being all triple-classed).
We don't intend to reduce
XP all that much (except perhaps to make the rewards more appropriate for creature difficulty and comparable to already existing creatures [which could go either way]). There already exists
xp-reducing mods for that.
There are so many powerful items now in my
game(I've installed an extremely complicated BWP game with the idea of having as many non-conflicting mods as possible while having the fewest errors), that I'm not too sure what constitutes excess [powers in an item. I seem to recall that the previous bp-balancer mod simply removed items. I therefore removed it from my install as I wanted a more comprehensive version of Zyraen's Miscellany mod which simply reduces the powers of items. For example, weapons that force creatures to do saves, should only have those saves activated no more than 25% of the time, the shield of Balduran should only be effective against beholder rays half the time etc.
That is also one of my biggest griefs with the BP-Balancer. It's idea of balancing is to randomly remove unique items, determined by a player selected factor. You'll be happy to hear that we intend to balance/nerf unique items rather than removing them, and while I'm unfamiliar with Zyraen's mod it sounds like we are thinking along the same lines.
The other problem is that there are a number of item-enhancing mods such as the Item Upgrade mod. I found that mod useful for improving some items in a moderate way(eg:- Unholy Reaver)
er etc.) but some items(such as the Kiihix spider figurine and the improved daystar(+8 to hit evil creatures!) were clearly
ridiculously overpowered.
As far as item upgrade mods go I'm as of yet undecided if they have a place in a mod like ours or not. Certainly many of them can be unbalancing, but when you install these mods you willingly accept such a risk. I don't see myself revising such mods in the overseeable future. For one there are way too many content mods that need balancing already, which in my opinion deserve it more than simple item mods. Secondly, many of these mods alter vanilla items, which we don't intend to touch in the first place (way too many potential compatibility issues). If someone would like to balance such a mod however they are welcome to contribute to our project.
Another thing:- Most spells in the standard BG2 game are hopelessly nerfed so that playing a mage becomes a joke as you have to rest countless times, once before each fight, and even then fighters are far more powerful. I mean, in a standard unmodded game, I remember lobbing fireballs at BG2 Throne of Bhaal creatures who would be barely affected by them. Fortunately spell_rev and spell50 mods allow changes to that, though I'm forced to choose between them sometimes rather than halfway between them. Anyway, what I'm trying to say is that some of the extra spells I've had added to my installation are by contrast to the BG2 standard spells, likely way too overpowered(eg:- firaga/blizzaga/thundaga/wind/bio) and require fixing.
I cannot stress this enough... Don't install Exnem's vault!
This mod has nothing to do in a balanced game and is one of the most frequently complained about mods in
BWP, before it was moved to the expert selection at least.
As for your point about underpowered magic in
BG2 I am not surprised that
ToB enemies shrug of a third level spell like fireball. Try throwing "Dragon breath" or "Comet" at them instead. From my personal experience my fighters couldn't hold a candle to my spellcasters in the later portions of
SoA and beyond. Nothing like a good "Dragon breath" for massive areal damage or an Elemental Prince or Deva for melee support.
when I'm usually around 
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