It's not that hard to make the areas look different, as such;

Add random crap such as;
abandoned buildings
beastmen
bones (why are there NOT carcasses laying around Thanalan especially?)
differentiation in plant types (color/shape/species)
wrecked caravans or carts
obvious man (or beast) excavated steps/cave leading to overlook of area on hill
ancient ruin-ish buildings (def feasible for Shroud)

Terrain colors and shapes;
when getting closer to zones, apply necessary color to fit upcoming atmosphere
random terrain forms (crater, giant crack in earth, carved by beastmen cliffs, etc.)
subtle color changes when near such things as water (greenish)
Ground color darkens or changes when it rains

I mean, yes this would take some time but in no way would these make it 'to large' as Tanaka previously stated why they were so copy/pasta.

DIVERSITY!!!