It would be great if the heroes in Elemental are not merely powerful units, but characters that the player really gets involved with. These are some ideas I have drawing from general fantasy themes.
1) Hero Groups
Heroes may belong to groups e.g. Knightly Orders, Wizards Councils, Royal Families, Assasins Guilds, etc. These groups are entities in the games that may become affiliated with factions permanently, or until some task or quest has been performed. They may switch allegience through the course of the game. Having buildings related to a particular group could increase your standing with that group, or increase that heroes from that group will work for you. If a member of a group if killed while in your service then that group might send another hero to average the fallen, or conversely become hostile towards you blaming you for the death. A player's hero who evolves to a particular level might be offered membership of one of these groups giving the player's faction and/or the hero certain abilities/advantages.
2) Legendary Items
When a hero is killed some of his/her abilities become instilled in a piece of their equipment. This becomes a legendary item and takes their name e.g. Crown of Bob, Ring of Dave, Sword of Simon, Wand of Mike (but with better fantasy names). There is then a natural instinct for the player to redeem the item and average the death of the fallen hero. If they are sucessful then can give the legendary item to another hero/unit, but obviously this item could be used against them in the meantime.
3) Interesting Story Arcs for Heroes
Betrayal, Redemption, Corruption, Exile. These sort of themes are fantasy staples. Whilst it might be aggravating to have a hero corrupted and defect from your faction, you'd be delighted to bribe away your enemies finest. A hero might be forced into exile in the wilderness only to return stronger. The corruption of good characters and the redemption of evil ones makes for much more interesting heroes and a game with a strong role playing theme as well as strategic challenge.
4) Returning Heroes
What I mean here is that heroes that you developed in previous games could reappear in subsequent games. As heroes evolve through the course of the game copies could be made of them at different stages. In a subsequent, game heroes that you have lovingly crafted in a previous campaign could turn up to fight for you or your opposition. I think this would really add a lot of replayability - you could take one of your old heroes down a completely different path, or find yourself facing the challenge of one strongest previous creations battering their way through your kingdom. This way each time you play you are building up an increasing rich world of colourful and diverse heroic characters. This could also provide the best of both worlds between 'growing your own' heroes and recruiting pre-existent ones. When the ability to add others players heroes into the mix, things get really interesting.
5) Relationships between Heroes
Another idea to create more sense of story around the heroes is have relationship between particular characters. Two obvious ones that spring to mind. First, Arch-Enemy, meaning that two heroes hate each others guts. The two characters could then have particular abilities that only come into affect when battling their hated enemy. If two heroes with this relationship were set to join the same faction then the player would be forced to choose between them, leaving the other likely to side with an opposing faction. The second idea is Endebted meaning that one hero fights alongside another until whatever the debt is has been paid. Going back to the Hero Groups idea, particular Hero Groups could be opposed to each other e.g. all members of the Circle of the Sun hate all members of the Black Cowl.
Often in fantasy games the character background and storyline has felt a bit tacked on to the game. It would be great to see features that work both from a game mechanics point-of-view and a involving storyline/roly-playing point-of-view.
Anyway, them's my thoughts...