I just returned from a B2B on Silhouette, both legs in Concierge class.
There are certain documented amenities associated with this class (Embarkation lunch, some freebies in the cabin, ...).
I had thought that this class was just really an excuse to charge more for a desirable cabin location.
However, I now know different. We had some on-shore issues (of our own making) that needed resolution. When we made these issues known to the Concierge (Taryn) dedicated to Concierge Class guests the issues were resolved within minutes, with no hassle on our part whatsoever. Also, the dedicated Concierge was able to arrange for a stateroom party for us. The Concierge is an officer, I believe, so there was no tipping involved. However, a lengthy mention of her was included in the post-cruise evaluation.
There are other, non-documented, benefits to this class that might occur such as Helipad sail-in/sail-away parties, acknowledgement of special occasions, etc.
I hope this helps.