In most strategy games, a piece of land is generally equally as valuable to everyone.  Think of Master of Magic.  A gold deposit, river square, or ocean square had the same value to everyone.  All resources were equally as easy to exploit by anyone.

So why not shake things up a bit?  I was thinking of all the different types of food resources that could exist in the game and what it would mean for expansion.  For instance, one civilization might start out with the techs to farm fertile land.  Another Civ might have the tech to catch ellusive fish on the vugged coast.  Another might be masters of redirecting the melting of mountain top glaciers, allowing them to farm the steppes.  Another could be masterful at animal husbandry.  Basically, each Civ would start out on different parts of the farming tech tree.  To gain other food resources, the player would have to research their way over to those other food growing/ catching methods which takes a lot of time and effort. 

Each region on the map would have different types of food growing methods.  Some would more than likely be more abundant than others.  For instance, a mountain valley might have a few "twilight bees," and some fish in a small lake, but would have much more glacial irrigation potential.  So essentially, the value of the land would be greater for those who had glacial irrigation tech, but not as valuable to those with other methods.

This creates an interesting circumstance in which different Civs can't use the same resources, thus diffusing the impetus for war between certain civs and increasing it for others.  If a Civ is incapable of managing a city in a mountain valley because they don't properly understand how to make a mountaintop irrigation system with melting snow caps, they are going to be less interesting in invading.  This creates a dynamic political landscape as well as a dynamic sense of setting.  A civilization doesn't simply expand into every niche of the world as soon as they can.  Instead, they prefer specific types of landscapes that have resources that they can exploit.  You would have rugged, brine battered shore-folk, windswept and barrel chested mountain-folk, and plains-folk.  

Gotta go to work, so I'll open the floor to feedback.