I feel an easier solution would be to redirect commoner traffic from high-profile hubs, such as the area in front of the Coin, the docks to Southbank, and to keep the tavern patrons away from the open tables and chairs. Let them roam from the bar to the stage to their own unsittable chairs/tables, rather than walk up to where players can congregate.
The spontaneous quest idea would be cool, but that could have some people just running around talking to every NPC ever, and there's already plenty of low-level quests. I'd argue we need more high-level quests instead, and spontaneous commoners is hardly the way to go about that.