I don't have a Highland gem card in front of me, but we came across this issue playing a couple of days ago. The gem card says something like, "You may exchange this card for 1/2/3/4 gold if you visit the Alchemist in the City."
Obviously, with the Cataclysm board there is no longer a fixed/permanent Alchemist in the City. He's now a Denizen that can pop anywhere Denizens can be drawn, and (if memory serves) he can actually remain in locations other than the City.
So if a character has gems and visits the Alchemist denizen, can he still trade them for 1/2/3/4 gold?
The answer that our group came up with was that if the Alchemist denizen is on the City space, then you can (per the explicit writing on the card). However, if you encounter the Alchemist denizen anywhere else then you can only exchange them for 1 gold, similar to alchemizing any other object.
Has anyone else run across this or thought about it?