A + 1 to Will Saves is only marginally better than - 2 to Will Saves?
I understand what you're trying to say, and for the most part I even agree with you, if you continue on the assumption that a player makes the toon, not the toon makes the player, and if the player is not bothered by missing 4 points, then excellent, however if he is bothered by the fact that all things being equal, that +1 is far preferable to - 2 then he will most likely continue to be bothered throughout the life of his character.
Let's say a 10 or greater is needed on a Will Save by the two, one 28 point wiz w/ 8 wisdom, one 32 pt wiz w/ 12 Wisdom.
The 12 Wis Wiz
needs a 9 or higher.
The 8 Wis Wiz needs a 12 or higher.
On a 20 point system that's 15% difference between making a save and not.
This will not "make or break" a build, necessarily, but it is certainly better to have the higher wisdom, even as a "dump" stat.