There are a few games out their with limited amounts of NPCs. One of them tried using virtually none. That game is now building NPCs to put in the game. Some games have far too many, some far too few.
We can find a comfortable medium with Planeshift. I really think using a well-defined trade and quest system will let the NPCs fall in place. As I stated before, I believe only a handful of NPCs per town is all that is needed, if a few new skills are implemented.
Giving power to the characters is a great thing, but there needs to be an NPC support system behind that maintaining the structure of the trade and quest systems.
Thanks!