I'd say it's reasonably well balanced in most cases. It's obviously of much more use to a rogue than to a fighter, for example, but overall, I think most classes are better off on spending the 10k on something that gives a big boost in one area they're really bad at, than a tiny boost to everything... 9k will buy you a +3 cloak of resistance, after all.
Just don't ever let a high level character make both a luck-stone and a pale green ioun stone... for a non-spellcasting class, that's like going up a level for 30k (minus the extra hitpoints)