Kristoffer, although I agree with you about how some units are "naturals", even "elementals" for what they do, carved in stone, and others being unpredictible surprises, maybe the way experience and growth of units in the game could be expanded a bit?
I personally find a lot of pleasure in watching a favorite unit evolve, over a long game, and I think there's more that could be done for long games.
A couple ideas for this are:
A blood/nature spell similar to Crossbreeding that, instead of creating a new unit, causes an existing unit to randomly mutate. It wouldn't alter the core chassis, but it could add extra abilities, hp, bodyparts, increased stats, etc. and it can also hurt a unit-cause afflictions, disease, lower the unit's lifespan, movement, kill the unit outright, etc. affected by luck.
It would be cool not only to cast it on your own units, if you have high luck scales, but to capture an enemy's unit in an MP and then cast the spell on the unit detrimentally, when you have bad luck, and send it back all deformed and useless, as a message.
Another good spell would be one that just gave a unit greater power, without having to cast Wish. Maybe a spell that greatly ages a unit, making some that would naturally grow more powerful over time, become a more powerful unit, and others to wither into dust.
I don't know about you, but I like the idea of double-edged magic.
Thirdly, I think the experience system itself could be expanded a bit, not necessarily to make it more D&D'ish, but still to allow some choices to be made about some units, to personalize them and customize them to whatever strategy you happen to be using. Maybe experience stars that a unit has earned could be "spent" on things? So that you'd end up with maybe a better unit, but that unit has less experience in his/her/it's new "role".
Finally, even units that you know who they are and what they're going to do, maybe they can still develope an occasional 'quirk' or become stronger than they started out over time. Not to change their basic nature, but to qualify/diversify it, and give those "elemental" units more *dynamic* personality.
Just a few thoughts from a Dom3 fanatic