16 WIS will be fine for Limited Wish, but it won't get you the top tier of stuff for actual 9th-level Wish (which requires 18). Wish is so random that you rarely get exactly what you want anyway, though, so it's not a big deal.
Aerie is a perfectly capable arcane spellcaster, but she doesn't get the higher-level spells as fast or in as large numbers as the single-class mages do. I often use her as a secondary mage to Imoen for more Haste castings and whatnot, but she can handle the job by herself as long as you don't mind the slower high-level spell progression. By the end of the game, she'll have nearly as many mage spells as the full mages, but she gets there a lot slower. The big issue with her is that her hitpoints are so phenomenally low. Any stray dragon breath or Horrid Wilting is likely to kill her outright, and you've got to be careful with your own fireballs as well.
The really nice things about Aerie, though, are the fringe benefits she gets from her classes. She can wear elven chainmail and use shields, the Robe of Vecna decreases the cast time of priest spells as well as mage spells, and she can load priest spells into a spell trigger or contingency, which gives her great versatility.