Right now in 3rd ed you only take an hour to memorize you spells for a day. You could bring back an old rule from 1st and 2ed edition on spell memorization times. In these older systems you had to rest for 8 hours (just like now) and then memorize spells at the rate of 1 spell level per 15 minutes.
The 18th level cast a 9th level spell yesterday, he needs to spend 2 hours and 15 minutes to re-memorize just that spell. This will make high level caster think twice about burring through all of their high level spells and having to spend the next 3 days doing nothing but re-memorizing spells. Add in random encounters and watch them worry about if every spell they cast is necessary. I would have sorcerer-types spend 15 minutes per spell slot level to refresh it.
The spellslinger remains powerful but allows the fighter-rouge types to shine in comparison during a fight.
The 18th level cast a 9th level spell yesterday, he needs to spend 2 hours and 15 minutes to re-memorize just that spell. This will make high level caster think twice about burring through all of their high level spells and having to spend the next 3 days doing nothing but re-memorizing spells. Add in random encounters and watch them worry about if every spell they cast is necessary. I would have sorcerer-types spend 15 minutes per spell slot level to refresh it.
The spellslinger remains powerful but allows the fighter-rouge types to shine in comparison during a fight.