Just curious, could you provide an example of how you would make the two fundamentally different? While I don't see any particular reason why they should function different, game mechanics-wise, I neither would have a problem if they did.
Personally I think that stat dependence and general theme/appearance is sufficient to distinguish the two, and having them work on the same resource (AP) instead of having a separate resource such as mana specifically for spells allows for greater balance between the different playstyles.
I'm just not sure why you would choose to use the word 'shallow'. Making the spells work in a mechanically different fashion wouldn't necessarily add gameplay 'depth', tacking on additional requirements for spells would simply give the illusion of complexity without actually contributing to the gameplay.
While I understand that having this objection doesn't necessarily mean you have an alternative in mind, if you could give an example of what you mean maybe we'd be able to understand you a little better.
