Absolutely worth the cost - amazing trip. DO NOT bring the kid along though as it is not a child friendly place and if you were in the cabin next to mine that I forked out $20k and I even heard a sniffle, let alone a cry from a kid - I would have to throw the kid and mama from the train!
It's a sophisticated black-tie type of trip that I'm sure they won't allow kids on anyways? But for you and your significant, there really are few other romantic trips out there that compare to this voyage! Even with the big upgrades, it is very beautiful, but small cramped cabins and you must really want to spend a lot of close contact time with your significant other. Dinners etc as mentioned are black tie and is just superb! Have fun!