Server Monster/Animal Spawns At Low Frequencies

Hello, I recently made a new work using the tool WorldPainter to create a hill-like terrain world for my new server and removing every plugin in my directory and configurating the bukkit.yml I can't seem to put my finger on whats going on here, basically the mobs in my server are not spawning as much as they use to.

In conclusion, what do you guys think could it be the world causing this? a bukkit error perhaps? some lost configuration that I missed?

bukkit.yml
http://pastebin.com/KxQyiGAD

The Highest Point In The World "The Spawn"
http://tinyurl.com/b9zjf3s