I like Sorcerer. There are a lot of imperative spells on Arelith, though, and I feel like the class currently lacks diversity because everyone is strongly incentivized to go divine sorcerer with a spellbook that is laid out more or less as follows:
9 - Gate, Timestop, Mord's
8 - Gsanc, Premo, *
7 - Shadow Shield, Spell Mantle, * (Arcane 7 is the worst base spell circle)
6 - Mass Haste, True Seeing, IGMS
5 - Energy Buffer, dismissal, *, *
4 - Imp Invis, Lesser Breach, Stoneskin, *
3 - Clarity, Haste, Flame Arrow, *
2 - See Invis, UV, Darkness, Balagarn's, Web
1 - Grease, Mage armor, PfA, True Strike, Ironguts
Giving Sorcerers +1 spell per school - the scaling Favored Soul and Shaman have - would go a long way toward allowing Sorcerers some versatility. If the concern is that this will make Divine Sorc oppressive (which I don't think it will, but I dislike that build and am very sick of all possible improvements to sorcerer being gated behind "but what about the increasingly-common synergy that'll give sorcs 14 uni and 14 dodge AC?"), then make divine shield cancel EMA. Having one dip archetype that's strictly better than all the others kills build diversity, and "caster stat to AC" has always been a problematic mechanic in NWN.
The most noteworthy change is granting access to their spell focus's capstone 9th circle without sacrificing major utility, and makes buying the buffs per school on 8, 6, and 5 feel less innately restrictive.
Shuffling some currently 6 and 8th circle spells to 7 would also feel very very nice: dropping Nybor's or Otto's (currently there are no enchantment spells on 7), or being able to take greater dispelling/breach on 6 or 7 would enable sorcs who want to commit to the counterspelling specialty to have a very potent niche.
Below I'd like to outline what I think the standard spellbook of a 26/4 Sorc/whatever would look like for Evocation and Enchantment focii under the proposed change. Remove the last spell listed for every level to see the current book.
9 - Gate, Timestop, Mord's, Dominate Monster
8 - Gsanc, Premo, Mass Charm, Otto's
7 - Shadow Shield, Spell Mantle, Protection from Spells, Banishment (feels bad man)
6 - Mass Haste, True Seeing, IGMS, G.dispel.
5 - Energy Buffer, Dismissal, Mind Fog, Lesser Mind Blank, Daltim's
4 - Imp Invis, Lesser Breach, Stoneskin, Evards, Remove Blindness
3 - Clarity, Haste, Flame Arrow, Negative Energy Burst, Sound Lance
2 - See Invis, UV, Darkness, Balagarn's, Web, False Life
1 - Grease, Mage armor, PfA, True Strike, Shield, Ironguts
and Evocation:
9 - Gate, Timestop, Mord's, Iceberg
8 - Gsanc, Premo, Sunburst, Incendiary Cloud
7 - Shadow Shield, Thunderclap, Bigby's, PW:Stun
6 - Mass Haste, True Seeing, IGMS, Acid Fog/Bigby's
5 - Energy Buffer, Dismissal, Lesser Mind Blank, Lesser Mantle, Darkbolt
4 - Imp Invis, Lesser Breach, Stoneskin, Evards, Remove Blindness
3 - Clarity, Haste, Flame Arrow, Negative Energy Burst, Sound Lance
2 - See Invis, UV, Darkness, Balagarn's, Web, False Life
1 - Grease, Mage Armor, PfA, True Strike, Shield, Ironguts
More options, but not a lot more mechanical power.
It also means that when new spells get added, almost every spell focus has a spell they could eschew on every level, which makes the class easier to scale power-wise with new content, which currently only a few focuses can afford.