Li Shenron said:
The extended casting time most of the time is not a big price to pay. The biggest price is still the increased level slot, and of course the cost of a feat. With this in mind, there is absolutely no balance problem if you allow the spontaneous casters to Quicken their spells.
I think balance is extremely broken with Spontaneous Quickened spells.
I think the Arcane Preparation feat is broken with regard to Quicken Spell (which is the only real reason to take the feat). Having a prepared metamagicked spell just to cast it as a Standard Action as opposed to a Full Round Action is not very appealing as a feat.
The reason I think this is broken is things such as:
Round 1) Quicken True Strike, Vampiric Touch (or other touch or ranged touch attack, especially one without a saving throw and/or spell resistance)
Round 2) Quicken True Strike, Vampiric Touch
Round 3) Quicken True Strike, Vampiric Touch
Round 4) Quicken True Strike, Vampiric Touch
Round 5) Quicken True Strike, Vampiric Touch
Round 6) Quicken True Strike, Vampiric Touch
Wizards (or Clerics or Druids) really do not have these types of options with the normal Quicken Spell feat (unless they want virtually no 5th level spell slots available for anything else).
I suspect that when people do not see balance problems here, it is because they have not yet played a character on the receiving end of the combinations that Quickened and Spontaneous magic can achieve.