I have a suggestion that has received mixed reviews from my peer group, to explain Unholy Blight and Evan's Spiked Tentacles.

Vaarsuvius was Neutral Good in this comic:
http://www.giantitp.com/comics/oots0011.html
That's how Unholy Blight worked on vir despite vir alignment as True Neutral should have allowed V to overcome it rather easily, if not bypass it entirely.
What pushed V into True Neutral?
http://www.giantitp.com/comics/oots0020.html
Evan's Spiked Tentacles of Forced Intrusion.
Then the Chimera screamed out "the horror... the horror!" V was shocked and guilty, though, because of vir's lack of emotional involvement at this point, did not share this with the rest of the party. Vaarsuvius forsook Conjuration and made it vir barred school, instead of what was previously V's second barred school, illusion, which explains why V hardly ever uses this school and is actually behind Elan as far as that school is concerned. Invisibility was also not cast until after the Linear Guild was dealt with the first time, so V could well have gained a level since #20. V does later say that he chose Conjuration as his barred school before "the rules of the universe have since been rewritten," but probably ve simply didn't check the rules in the 20 strips from the 3.5 update to vir's attack on Trigak. This explains the shift in V's alignment as well as why ve no longer uses Conjuration. It also gives us sort of a prelude to V's second (possible) alignment change with Familicide, which is from Necromancy, Conjuration's evil twin.