Leatherhead
Possibly a Idiot.
That's how 4e handled it!The solution seems obvious: Make the spell lists unique to each class. I mean. There's no sensible reason why a Cleric would need access to a list of Wizard spells, for example.
This would also be beneficial in that it would require that spell lists contain only unique spells. It would make the bard more interesting since they would have unique bard spells. The wizard would have unique wizard spells etc. etc.