There is some new content regarding a few of the new joinable NPCs once you get to a certain point in the main story and have access to Baldur's Gate. One is major and part of a questline and the other is a small encounter.
there are some new items in the city, the big time mage at that sorcerer's shop has some new items and spells and there is a sling +2 ( kinda, it gives +2 to hit and +0 to damage) in the city as well
its in the inn below the blushing mermaid inn, in a chest right beside the stairs on the second floor
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