While the class has theoretical Tier 1 potential, I still think the extreme hassle of actually playing one would prevent it from ever reaching its true potential until the higher levels, i.e. until a spell won't dissipate during a normal adventuring day.
For instance, at level 1 a Sha'ir will need to get new spells every hour, or basically constantly have his gen fetchign spells to replenish those that dropped out. (And seriously, saying the dissipated spells count as cast is ridiculous.)
Now a strict GM could ask a player to actually DO that paperwork, and also mention every time the Gen is sent out. And that... would just kill all the fun. And with rising levels, the player would potentially have to do more and more paperwork, what with rolling every fricking interval for the Gen to get the spell.
That's a mechanic that just doesn't work, as written. The only way to play it would be to say, hey, get your spells in the background, I don't give a damn until you get a spell you don't know or a divine spell.
Also, the Diplo check:
Let's say the Sha'ir has 18Cha at level 1, and 4 ranks in Diplo: The DC is 20. The bonus is 8, +1 for level 1, +2 for a known spells, -2 for a level 1 spell = 11. That's just over 50%. And don't tell me I should take a crappy feat (with the possible exception of Nymph's kiss) to improve that chance.
At level 10, the Shair has, say, 24 Cha, and 13 ranks. That's a +20 bonus, +2 for spells known, +10 for Shair levels = 32. So at level 10 you can definitely get a level 5 spell known (-10 to the check). For an unknown arcane spell, you still get it. For an unknown divine spell you're back to rolling, after having to wait for X hours for the spell. (And a 5th level spell could take 11 hours to get!)
So while that mechanic is marginally better than a Truespeak DC, it still sucks.
The class is interesting, and has high theoretical potential, but only if you actually REMOVE all the hassle involved with it. In which case it's just a Tier 1 wizard with access to some divine spells.