How about adding non-combat abilities to some of the lesser used creatures?
Get double gold from winning a combat
Get double experience
Get double gems or guaranteed brilliant gen
Use only half energy in fight
Merchant discount skills
Plus critical % to others in team
A useless legendary such as the alchemist can have multiple of these skills like both double gold and double gems. It fits him. I have 3 alchemists and can't be bothered to evolve him cause he's so weak. But f he has these buffs, I might use him more.