I would. A second city would be content extension, giving a new area of large size with more quests, more NPCs, etc. A stronghold is a new gameplay layer, with construction options, recruiting, simulation strategy elements, etc. Given a choice between a new gameplay layer to give me something different but meaningful to do in a game, and content extension where I just get a lot more of normal stuff, I think I'll pick the gameplay layer every single time. Unless I don't like that gameplay element of course.