Interesting. I'm trying to think where spawn rates are different. I think perhaps Colonies has relatively more monster/undead spawns than most islands. Then again, it might just be that hordes are more noticeable on a small island with one turn a day!
Anyway, I think Colonies could do with a lower undead and monster spawn rate. One turn a day combined with some lengthy travel times can make them very difficult to deal with. I think it is a distraction from war and when war comes, if you suffer from spawns it can be a major headache to try and get rid of them.
Atamara possibly needs a higher undead and monster spawn rate. Atamara definitely feels like it gets off lightly compared to other places.