Not to derail the topic, but if anyone does use the suggestion I mentioned for their games. i would love to hear how they went and what all problems came up and how balanced it felt.
I only have our group and our play style, so have limited experience on how the rule works. Beyond how it works for us.
It's been many many months since I've posted over here at the Paizo forums but yes, our group has been using a very similar house rule through Curse of the Crimson Throne and we're using it for Legacy of Fire using the Beta rules. There were a couple of additional caveats the DM added, Practiced Spell Caster and Mystic Theurge were out. Also, multi-class casters gain the class benefits like domain, channeling energy, school or bloodline powers based on their actual class level. They only gain extra spells and caster level. In both cases, I was the multi-class caster.Our Party for Crimson Throne:
Sorcerer (with Fighter cohort)
Cleric of Calistria/Rogue (me)
We made through fine. The AP was challenging and my character really didn't feel over powered.
A better analysis is the party for our Legacy of Fire Campaign:
Cleric of Sarenrae
Cleric of Asmodeus/Sorcerer (me again)
Compared to the straight class casters they have much more powerful spells than me. What I ended up with is versatility. It's sort of like the old sorcerer vs wizard debate. We really don't have that much extra healing in this case.
BTW, in case any one was wondering how those two clerics could manage to work on the same side. We manage with some good natured in character bickering ("That's Evil." "No, it's not. If it was Evil then it wouldn't be legal.") Don't want to do any spoilers but it kind of makes sense (so far) in Legacy of Fire if you look at Golarian mythology.