I'm thinking it through. Might take a while.
The easiest would be to just use Bard spellcasting, I guess, because it works fine. Perhaps put it on the Cleric's hassis? Something like Cleric hassis and class features, but Bard spellcasting with Cleric list? Maybe I'll add Archivist's class features to the mix.
Do note that by pushing back the level you get your spells, you're also pushing back the level at which you get the various Remove ___ spells. Unless you adjust monster CRs accordingly, this will have the unintended affect of leaving the party more vulnerable to energy drain, paralysis, and the like for several more levels.
Probably the easiest way I can suggest for dropping tiers is to give each class a very nailed down spell list, like the war mage or beguiler, and let them cast off of it spontaneously. Be sure not to actually make it too good, though. If you give them all the win spells, then you haven't really weakened them. One thing to keep in mind is to make each character primarily only affect one type of save, so they can't just switch to affect a weak save round by round. This will make it more important to have well-rounded parties, which may be good or bad.