I'd like more people in the towns too. If they could open new subquests, create new shop options, add
precious hints and stories it would be even better.
A bad thing for me, however, is that when you finish an Act all the previous NPCs become suddenly useless. I personally need more background story, happenings and gratefulness to really care about those citizens. More RPG deepness?
Random merchants would be interesting, but I fear that would simply end with.. merchant runs! Like MF but even worse as they're in town..