Don't you think that heroes goes beyond 100 should still have some reward?
Here is some idea.
Great strength: hero + 10000 fighting strength and takes half damage in adventure
Legendary adventurer : the adventure point recovers twice fast as normal
Resilience: hero +20 maximum health point and can survive even health point reduce more than 90 in a single battle, but still die at a single battle when health point reduce 100.