OT: For Pathfinder's Bestiaries - I needed 1 and 2, in order to get the full range of monsters I had before in the Monster Manual 1. I needed two and I'm happy with my investment, because they focused on different kinds of creatures. First one was more natural creatures and the second focused on higher level threats, I appreciate that split.
They also focused on different kinds of creatures for Bestiary 3, and I like that. I don't currently have a use for the B3 but if I ran a different cosmology or setting I would definitely pick it up.
I don't know what's in B4 yet, but I don't have any issue with them printing more books as long as they have good ideas left. I don't want to see a book of goblins with different roles, that we got with.. monster manual 4, 5 ?