Is Yacht Club worth the extra money? I would have to say YES.
It cost us about $1000 per person above the cost of a normal balcony suite. We arrived early for embarkation and were met by a butler who took us straight up to our room. It was a bit larger than a normal balcony suite with plenty or storage room. Very well appointed and the bathroom had a bath which was nice. We chose a cabin on the port side as we got better views when we were passing land from that side.
Yacht Club entitled us to the free mini bar, room service, daily newspaper, priority embarkation at ports, use of the Top Sail bar, our own pool, bar and spa on the top deck and dining in the L'Olivio restaurant. The service in all of these was impeccable and the food in L'Olivio was outstanding. I saw some people paying for premium wines but there was nothing wrong with the free wines they served.
Cabin was large and well appointed. Extremely quiet - we couldn't hear any noise from outside or adjoining cabins.