All NPCs should be able to say something, whether it's one line or whatever it is.
A good balance is what I want. Say... 50% interesting NPCs that you can talk to and 50% less interesting that only say some basic lines.
The numbers shouldn't be ridicously low though. Every house should have 1-3 people.
Also, "Depth or no depth".
It doesn't have to be like that... black/white, yes/no.