It's just very random, but Sef is right about the clerics, must kill em and not neglect the igloo on the hilltop...idk about the ratter, as I have spawned Tak without killing it.
Yeah, the shield is worthless, 'cept for looking good on the dollies...but if it sells well still, then wth? It's called farming. On top of that, gem drops usually don't suck there, so all in all, if you just want a quiet profitable session of killing gobs, why not?