"frequent travel also seem to reduce vice rate."

For laziness and drunkness only.

"if they become a bit corrupt, I stick them into frontline stacks and keep em fighting until they are either brave beyond belief and reborn saints or dead."

The vices that come along due to empire bloating is very irritating. I tend to get those money grubbing guys killed on the battlefield and appoint new ones (who again have short lifespans).