Maybe they get replaced by actual thieves and bandits, or monsters with a different theme for each district? I mean that's really the problem I guess right there. I don't want to see Baldur's Gate at high noon when everyone is running their daily errands, but the 3 am version.
I love this idea. Seeing the city at night, gittering stars and high dark buildings, exciting, full of opportunities and bandits.. yeah, I'd like that a lot..