I think NPCs should talk amongst each other or interact some way while not engaged, all the NPCs standing in the wards not doing anything are kind of creepy :p. People usually dont sit at a table at a bar and do absolutly nothing but stare into space :p.
EDIT: in addition, make NPCs close up shop for a few game hours and GO HOME or somthing, it would make the game a little more dynamic if you had to wait for certain times of day to talk to certain NPCs. You could have NPCs that come out at night and NPCs that are out during the day and Crackhead NPCs that are out all the time!