For mages/clerics/sorcerers you had the solution there, Baarvark. Best option would be a new menu window to select dairy spells and uses, and then when they use a bed/matress/activate rest all objectspells are deleted and the proper ones are adde to the player's quickbar, you can't trade nor throw away the objectspells. Number of objectspells/uses is based on player's intelligence (mage), charisma (sorcerer/paladin/bard) or wisdom (cleric/druid). Also magic items like some rings/amulets can add spells per levels.
Doing that we'd have a proper magic dnd system in divinity.
Problem would be, of course, the list of spells and their effects. That's something we should look into spell-by-spell
