In my opinion, there are a lot of lessons to be learned from previous 4x'ish fantasy games, their successes and failures.
One of the more important lessons, that I think has been neglected in recent titles, come from the early homm titles:
Basic Positional Audio to reinforce the sense of connection between unit and map!
The early titles had small loopable samples connected to many of the areas.
example: a hero was close to the coast, close to a mine, close to trees:
The following samples would play: crashing waves, the dink of picks on stone, the sound of wind in the trees.
This very simple system was in my opinion one of the most immersive features I've ever encountered in a non 1st person game. elemental could REALLY benefit from it imo. Its also a big challenge, since space (galciv2) has the advantage of being soundless, so the only sounds you need are explosions and pew pew pews. a fantasy map without sounds would plain suck 
