You make good points, Imaro. When I thought up the Rage/Spell(Rage) comparison, I had forgotten how complex the spellcasting system was in 3.5.
I've pretty much forgotten what our spirited debate is about, so let me regroup here.
It seems like we're really arguing over whether or not all classes should use a single system.
Your argument: because everyone uses the same system, there's no fundamental differences between the power sources. It might as well be named Power Source: Fun or what-not, since it's all push-pull-slide. A fundamental difference between the classes is defined by different mechanics.
My argument: because everyone uses the same system, there's only a need for a gaming group to differentiate between the sources if they see fit. WotC provides the base fluff for beginning groups to work off of, and experienced groups can (and will) take things into their own hands, describing the push-pull-slide of powers as they like.
We're edging really close to simulationism/gamism debate, which leads to madness. We might want to call it here.