Leveling up Heros with experience
So I think that you should be able to level up your heroes by gaining experience from attacks and defenses. For every building destroyed or troop killed in battle the hero would gain a little experience, it doesn't have to be a lot just a little bit to help with how hard it is to collect dark elixir, as you gain experience with that hero, then the amount of dark elixir needed to upgrade the hero the rest of the way will reflect how much experience is gained. Even if this wasn't available right away when you get the hero, if it was unlocked at a certain level, like 5 or 10, it would be pretty helpful.
