My goal is while inspired by 4e to try and do better than that.
I think HD expenditure should refresh and invigorate not just bolster resilience. Which is better emulated by recovery of both hp and some offensive energy.
Tie the spending of HD to getting back short rest resources ie you only get the one with the other... ie it might even mean you only get back your fighters CS die by spending HD. Yes after the battle a HD lets you gain HP and some amount of KI or a CS die or Spell Points or whatever.