My wife and I have been playing Caverna for years. We've played enough times that we're quite used to picking out each others' strategies and working to counter them. The game is NOT stale by any means, but the Forgotten Folk expansion adds a great complementary layer of intrigue to the game. The 8 Folk play quite differently from one another, and the many new furnishings make for quite a different game each time around. I highly recommend getting the expansion for anyone who really loves Caverna.
I will say that the price is a little bit high as I was expecting some more refined components like the original games resources made of wood and plastic. In the expansion, the new resources are cardboard punchouts which work just fine but are not all too exciting.