Is there any way that you could make the toughness enhancement based off of taking the feat rather than taking a class? Toughness is one of those feats that's supposed to benefit all classes equally. Here in DDO land it's now a highly desirable feat/enhancement chain for Fighters/Paladins/Barbarians/Dwarves while making it less desirable for everything else.
My suggestion is to base the class toughness enhancements off of base hit points. This makes it a more aggressive enhancement chain for fighter types but allows everyone the potential to gain some benefit from it.
ex.
- Enhanced Toughness I - AP Cost: 1 Requires a minimum of 10 base hit points.
Increases the total benefit you receive from the toughness feat by 5
- Enhanced Toughness II - AP Cost: 2 Requires a minimum of 40 base hit points.
Increases the total benefit you receive from the toughness feat by 10
- Enhanced Toughness III - AP Cost: 3 Requires a minimum of 70 base hit points.
Increases the total benefit you receive from the toughness feat by 15
- Enhanced Toughness IV - AP Cost: 4 Requires a minimum of 100 base hit points.
Increases the total benefit you receive from the toughness feat by 20