There are many builds that would benefit from this - not just multiple set stackers.
In fact, most set stackers are already sitting at +12 for their relevant stats, as Wis/Int are usually included in the relevant sets. (Swash, Arcanes, Monks, SS)
Additionally, most powergaming toons are Cha based - EDM melee/Ranged or FS/Sorcerers with Bard/Paladin/BG dips, and don't really use Int or Wis for much - Maybe a +3 Will save?
Putting Int/Wis as a cloak enchantment would greatly help several non-set builds, such as Monk dipped longbow rangers (the Quiver from drow castle was changed from +12 Wis to +12 Dex), non-set Swashbucklers, Wizards, non-set Monks, and Clerics. I think closing the gap between set and non-set users is a good, and not a bad thing.
It would also be mutually exclusive with +Cha, so a character will have to forego +12 Cha to choose Int/Wis.
As Cha requires a P K F F runeword, I suggest Int and Wis be roughly equally as expensive to balance the 3.