So ask any optimizer and they'll almost always tell you the same thing: in 3.5 classes that prepare spells are better than spontaneous spellcasters. It's generally not thought of as even a contest. There's a few reasons for this (never mind that prepared casters usually get better class features than their spontaneous counterparts), but the most often quoted are the slower casting progression and lack of versatility. All spontaneous casters get for their loss of power and versatility is ease of play. My players just finished a campaign with an Archivist and a Druid and they ended up fatigued by all the extra work. They like the idea of spontaneous casters but they don't like feeling like they're being punished for choosing a clearly inferior class just because they don't want to waste everyones time choosing spells.
Of all the things I have thought to try to fix this imbalance, the simplest seemed to be speeding up the spell progression of spontaneous casters to match the progression of the preparatory spellcasters. There had never seemed to be a good reason for this anyway unless Wizards really overestimated the value of spontaneous casting. This seems to help get those spontaneous casters on almost the same foot as prepared casters. I actually think they still wouldn't be as good, but it would close the gap significantly, which is what I'm looking for. Does anyone have any experience trying something along these lines? Or any thoughts or other ideas about closing this gap?
Oh, and I know that "spellcasters don't need any help." I find the tier system instructive but take its recommendations on party composition with a pretty significant grain of salt. I'm not interested in how the Sorcerer stacks up against the Barbarian, because the two serve totally different roles. I'm much more concerned with how it compares to the Wizard. In my mind, the two should play differently but not have such a significant gap in power.