I love the feature of costumes, but I'm sad about its price and the stat bonus.
I believe that in the future(Yes, I know that I don't know what their other costume plans in the future, but I'm saying this to like prevent it? I dunno. Just wanna speak up),
each costume will have its own unique stat bonuses, and that would suck so bad because what if you want Costume 'A', but you want the stat bonus of Costume 'B'?
I suggest 'auras' (like flame like thingies that goes around a character.) instead for 'stat bonuses' that can be equipped on 2 new equip slot when your hero is wearing a costume. At least with that idea, you can wear the costume you want and the bonus stat you want. (Auras can have one stat bonus each)
Though if this will miraculously happen, I would happily buy a costume for 350~400 gems depending on design or something and aura roll ticket for 100 gems each. (Yes, I'm saying aura 'roll' because I know you like us to pay more gems and I'm desperately wanting this to happen because I like COSTUMES! :'D)