I thought this thread was about fixing orbs
I don't see the problem resulting from sleep, exactly. I see the problem resulting from someone focusing heavily on Wisdom and creating an auto-failure for any non-eilte/solo monster, and near-guaranteed failure for elites and solos.
The potential to impose a -10 penalty to saving throws is way too good, simply by the fact that saves do not scale and remain a base 10+ success at any level. This does not even include Spell Focus.
I think my fix for this is to simply add half (instead of full) Wisdom bonus as a penalty to saves. This means that even with heavy investment, the most a character is getting out of this is -7 (30 Wis, Spell Focus). I think I can live with that.