The part I liked about the Command Card aspect is that it forced tough decisions. There's a trade-off for bringing heroic dudes - in the loss of a command card for other units and/or command actions.
Here, why wouldn't you bring one of these guys? It's not that hard to find that amount of points, and there's no downside. So every battle will probably have a Hero or Legendary Unit in it, which feels cheap. If I see something "heroic" on the table, it shouldn't just be because there's extra cash lying around.
Even if we stuck with these rules, what if we made it so you couldn't *buy* these guys, but you could promote them? Or at least limit how often you could buy.
Legendary Unit
Any non-elite unit that survives a battle after eliminating two enemy units may be marked Veteran.
Any Veteran unit that survives a battle after eliminating two enemy units may be marked Legendary.
Eliminating an enemy in this case means that the unit was the only unit that dealt damage to the enemy on the turn it was removed from the battle.
Once per turn, a Legendary unit may re-roll one die on any courage or combat roll. This is in addition to any Command Card effects.
Your opponent may also name a unit as Veteran, or a Veteran unit as Legendary, if they feel it justified.

Hero
Cost is 200 points. You may only buy a new Hero on "even" rounds of a Campaign.
If a Hero survives a battle you may take them on the next battle at no cost.
A unit with a hero deployed is +1 courage and does one extra hit in combat.
Anytime unit with a Hero deployed is about to lose a Red damage box, you may remove the Hero to prevent that damage. This does 1 additional damage to an engaged enemy unit.
Heroes are deployed after all units are placed, but before standing orders are determined.
If two opposing units with Heroes are ever engaged, the Heroes duel. The units fight as if there were no Heroes deployed until the duel is over.
Dueling Heroes each roll one two dice. If one Hero beats the other Hero's roll by 3, that Hero wins the duel and the losing Hero is eliminated with no other effects. If one unit routs before the duel is over, the duel ends in a stalemate.
Only two heroes can duel at once - others wait their turn.