Personally, I take the opposite view of most people here and would not allow wishing for feats.
My reason is simple.
Feats are generally acquired once every three levels. They are rare. They are special. They define a character. They often have built in chains that prevent certain feats from being used in conjuncture with other certain feats for some classes.
Just because WotC and other D20 companies actually have written about 300 feats overall and everyone and his brother wants to try a lot of them out with their characters does not mean that PCs (or NPCs for that matter) should be able to get more than their allotment.
Fighters get no spell casting capability at all. Instead they get feats.
Allowing Wizard, Sorcerers, and Clerics the ability to trade experience for feats lessens the Fighter. IMO. And at 5000 xp, that is less than a third of a level at 17th level. Lower level characters lose more experience than that dying and getting raised and gain nothing for it.
High level spell casters have enough power without giving them more feats. Again, IMO.
Also, it basically takes 2 Wishes to increase an ability score modifier by +1. That results in a 5% increase in ability for certain abilities. In order to balance this, one feat adds 100% ability (i.e. you gain the ability to do something that you could not do). So, if your average +1 ability score modifier affects 10 things (skills, combat abilities, AC, hit points, saves, whatever, and 10 is probably a little high on average), it means that it is equal to a 50% increase in one ability (skill, whatever). Hence, power-wise, it would take 4 or 5 wishes to equal one feat (rough approximation). YMMV.
So, it sounds like power gaming to me. Bad enough that wishes allow ability score increases in the first place.