What about a solution like this for Incorporeal Spells or other ‘specialized’ cases to have Adaptations for these things:
Adaptation: Ethereal Spell
Requirements: Arcanum as a trained skill
Adaptation Cost: CTN +2, Speed +2 (+3) <-- Subject to changeBenefit: You may utilize this Adaptation on any spell which requires an attack roll and currently does not affect Incorporeal Creatures. The spell is now able to affect Incorporeal Creatures at full effect.
This enables people to choose which spells they want, while still devoting a resource to being able to handle some fringe cases in a way that makes sense for their character.
John