Critters or people running around would help - depends on what the engine can tolerate given memory constraints. If in a jungle, show some leopards or monkeys or whatever lore creatures exist. If a savannah, lions and elephants or w/e. Basically, show the wildlife.
Vary the amount of tile types and versions of each type to broaden the look
Have the land become more alive as ZOC's expand - not just turn green, but show signs of civilization beyond the random caravan on a road. Tiles closer to settlements or resource nodes should show how civilization is expanding. See mechanics comments below.
Tiles on ZOC borders should show some kind of hybrid tiles - ideally there shoudln't be an immediate crossover from green kingdom to dark fallen but something that indicates it is a border tile and has a hybrid look. I'm thinking of where the blight meets non-blight from Wheel of Time.
Hybrid of Civ
Instead of managing the tiles outside a settlement, have the tiles incur some kind of modifier to food, materials, metal, crystal, etc. For example, a city placed near a forest should receive some kind of materials benefit from the forest. A settlement near mountains or hills should receive something to metal. Settlements near standard plains a food modifier.
Those settlements that incur positive modifiers to the settlement should start to reflect that activity. Using the forest example, a city receiving benefits from forest tiles should see some logging type buildings and activity happening within those forest. Plains should start to see some mini-farms and such.
I think it would be cool to see how settlements start to change the landscape with human activity. The world would start to come alive. Just dreamin'!
I like your ideas. Having the world literally come more alive would be nice. Having some animals on the map would be cool especially if they can integrate lore into it.
Really emphasizing the return of civilization to your lands would be a nice touch as well. Signs of human activity like little cottages popping up or hunter's cabins would be fantastic.
Also, I think your hybrid Civ style idea is pretty good. Make terrain matter more.
Oh and I really hope that the seas and oceans aren't totally useless this tiem around. I'd love to see fish and whales and other marine life.