Seriously, did your wizards prepare nothing but Comprehend Languages, Magic Mouth, Tensor's Floating Disc, etc? If so, I guess you better have hoped that situation came up. Now they can use that spell without even wasting space having to memorize it.
This sounds more like a complaint who from someone allowed wizards to cast spells out of their spellbooks whenever they wanted, instead of actually having to memorize them. If so, well, that wasn't in the rules either, so what's to stop you from houseruling the same thing in 4e?