Catching up after a period of absence from this thread.In the old days they had only 1d4 hit points, which made them a suitable challenge for brand new first level characters. Goblins had 1d6. Once the party advanced to taking orcs, which have a whole hit die, kobolds could be forgotten. In 3.5, kobolds have a full hit die, so they're useless.
I've always thought of the duergar as the chasidim of dwarves.
I'm still catching up, so more later.