Hmm... I see: Limited wish isn't worth more than 1 Con - the problem is, that wish has two versions: The spell-duplication wish (which isn't worth more than 3 Con), and the bigger, perma-effect wish (and, of course, the "screw yourself"-interpretation one), which is, at least in my opinion, worth much much more - like 5 Con or down to 1 Con.
Hmm. It used to be, in previous editions, that you could do certain effects (like heal the party, raise a dead creature, or move them out of harm's way) without incurring the "holy crap I need to rest" thing, and that anything else took such a strain on the caster's body that he was laid up for 2d4 days. I'd certainly add duplicating spells to that list... let's say
Healing the party, raising a dead creature (resurrection, not true res), moving the party, duplicating a spell*, creating a nonmagical item, undoing a geas, or transporting people are all lesser versions and only incur 3 points of Con damage; and
Increasing stat scores, creating magic items, or altering reality are greater versions and incur 5 points.
*And, of course, if the spell has ability burn of its own, it's added to the cost of the wish.
Then you could do the same with limited wish - duplicating a spell or reversing a geas costs 1 Con, and any other effect is 3 Con.
