This is a dangerous usage. Bascially wishing for a higher level.
If I were the DM, the result will mostly depend on who is granting the wish spell.
If the caster himself cast the wish, I would drain 5000 XP +3000 XP from him and create an Orange Ioun stone in his hands. Or perhaps a custom item such as 'Headband of Practiced Spellcasting' that grants free use of the Practiced Spellcaster feat. I might even, depending on the situation, make the items take the form of a magical tattoo, so that it cannot be stolen or lost (but it can still be disjointed if things really get out of hand).
If the wish was granted by some higher power as a reward, I would have the higher power create the items for the character (without actually using the wish spell-like ability -- IMC spell-like abilities that emulate spells with XP cost drain XP from the user). If the wish is granted by a mostly benevolent power, I would give the character the best possible result, within reason -- most likely a magical tattoo that functions an orange ioun stone. If the wish was granted by a malevolent power, expect the power to twist the wish so that it requires the least work from itself -- and inflicts the most suffering on the character, simply out of spite. The power will likely just have a minion steal a orange ioun stone or similar object from some other archimage -- or even better, steal an orange ioun stone that the archimage accidently cursed in the creation procedd, as so decided not to use...
If the wish were granted by a non-sentient object, the most straightforward method will be used. The wish will likely teleport the nearest caster-level boosting object into the character's hands. If that object actually belongs to a level 35+ archimage who is now wrathfully scrying for his lost property... well, tough luck.
And finally, if the character were trying to coerce wishes from outer-planar creatures, such as an djinn, efreet or even pit fiend, well.... at the very least (if a djinn who isn't too angry), the wish will fufill the caster's request by turning the character into a wild mage -- each time he casts spells, add 2d6-7 to his caster level. For the others, transforming 1d3 of the character's non-caster class levels (if any) into levels of tainted sorcerer (UA) sounds nice. Of course, there is always the time-tested classic of plane shifting the character into the Tomb of Zago-ephot, advanced 156HD hecatoncheires, which is buried ten thousand miles beneath the Grey Wasts of Gehenna.
"I wish to become a more powerful spellcaster!"
"Granted," plane shift, teleport "Now all you have to do is defeat little Zago-ephot here, and you will most certainly become a more power spellcaster in no time at all." Open door, push character inside, close door. Oh, did I forget mention the fact that the entire inner-sanctum of the Tomb is under a diety-level anti-magic field?
So, for your answer. Yes, such a wish does indeed exceed the 'safe use' terms of a wish spell. If I were the DM, I might, depending on the situation, use other methods to grant your character the effects of his wish, without giving him a straight, innate, caster-level boost. However, making such a wish will always be dangerous to your character, and reality also might choose to punish your character for his greed.
Good luck with your wish spell!
Yanei Wu