I'm not entirely sure what resources you could have in a swamp... perhaps some healing components, perhaps some crop that grows vastly faster in swamps, maybe some creatures that are worth hunting that only spawn in large bogs...
I'd suggest crocodiles but that's not really thematically appropriate.
Desert currently has clay-pits, but maybe have the deserts spawn scorpions which can be gathered for poisons (or sting people who move slowly or stay stationary near them for too long).
I also feel that deserts and swamps shouldn't really be terraformable like grassland and forest. Even building a paved road shouldn't really be possible if it's a sand desert as the road would be buried relatively quickly... Possibly make such areas larger as well so they can block off large corridors.