Cleon
Legend
Cleon's reluctance for Con drain makes me think we could use a Con reduction in a different way...
Instead of a Con drain for each granted ability, perhaps the Vizier's Turban imposes a -1 penalty on the Con score for each spell level. (It might bear a resemblance to the Quintessential Wizard feat that lets a wizard temporarily burn Con points to boost their spells.) The Spell Resistance cost would be a one-for-one cost.
Cleon's point would still stand... a -5 penalty to Con (much less any ability score) might cause any player to wince, but a bonus spell and Spell Resistance seems worth it.
Alternatively, we could maintain the hit point drain but apply it in a similar fashion... the wearer/host would suffer a unique -2 per spell level penalty to his total hit point score.
I'd like that approach better. Certainly the penalty should be something that can't be removed as long as the Turban is worn, like the negative level some magic items impose on inappropriate users.
A -5 Con penalty might still be too much. That's -2 or possibly -3 hit points/level, plus the same penalty to Fort saves and Concentration skill penalties. That's a lot worse than the original's -1 hp/level. The worst (10 hp) cost would be passed at 4th-5th level. (-3 hp/level at 4th level or -2 hp/level at 5th).
So, how about going for a straight HP reduction/penalty like the original?