Maybe not good Idea, but what about give to ALL unit one basical trait depending of what there are.
I mean, sometime the game is quit funny : killing ifrit with fire??? Or undead can become sick???
So what about give too each race one unique trait capacity in addition to the 3 normal trait?
For exemple undead immune to sick; dwarves receive more money; knight got 25% skull damage résistance; naga immune to poison etcetc…
Have a good day.