Quote Originally Posted by Andezzar View Post
Neither Enhance Spell nor Empower Spell actually increase the spell's level
Yes, I do know that. I was speaking inexactly.

To get the benefits of either feat however, you need to either prepare that spell in a higher slot or expend a higher slot (in case of spontaneous casters). You can find those rules in the description of the feat type.
Except that those rules are not universal. Specific trumps general, and we already have multiple instances of this very rule being overridden by a specific metamagic feat: Substitute Energy is just one of the metamagic feats which explicitly does not require a higher-level slot.