I think it would be interesting to see respec tokens.
Respec (respecialization) token will allow a player to reassign an x-number of stat scores from a hero, following a 1-1-2 ratio of att-def-HP.
Let’s say we create 1*-5* tokens, allowing to reassign 10-50 stat scores on a hero. For example, I have a Grimm with 716/531/1132 stats. I apply a 3* respec token (30-stat scores). I remove 16 from attack and 28 from HP (worth 14 units because of conversion), 30 stat scores total, and invest them in defense. Now, I have a Grimm with 700/561/1104. A token can be used only once on each hero, so the most possible variation could be 50 on att and def, and 100 on HP. That would prevent ridiculously skewed heroes.
I think it would liven up the gameplay with different setups that players come up with. Think of some of the heroes who are so skewed in their stats (Scarlett, Gormek etc.). Now you can have your favorite hero with more balance.