I cleaned up some level see sawing in the 2nd half (always defaulting to the higher XP totals). I jimmied the 1st level spell totals adding one at 2nd and 3rd levels and removing one at 5th. I also added 4 at 12th level instead of giving the illusionist 6th level spells (a take on the AD&D's illusionist's ability to switch out a 7th level spell for 4 1st level MU spells.
I think the thief's special abilities stand as written (reading MU scrolls at 9th level even). Instead of making magic items I think the character could make illusions permanent or "real" or something. Sneak attack OR biding time.
Spells are posing a problem: I think I should add darkness, continual darkness, and true seeing (I don't know how that spell reverses). I think animate dead, fireball, and maybe lightning bolt and cloud kill need to go. I'd like to drop comprehend languages and read magic and let the thief abilities do the work but I'm not sure how to get new spells to the illusionist.
Also, should the illusionist be allowed leather armor?