When I click on the link with the upgrade offer, below is exactly what it says regarding the perks you'd get if upgraded to YC (you get them ALL):
In just a few clicks, you can submit an offer to upgrade your stateroom on your upcoming cruise.
Browse through the stateroom options below and select the amount you're willing to pay for an upgrade to each. Making offers on multiple rooms will increase your chances of getting upgraded, but you'll only ever pay for one upgrade.
We'll notify you via email if your request for an upgrade has been approved. If your offer is accepted, you'll be charged for the upgrade. If not, you pay nothing and keep the stateroom you have.
Offers are priced per person based on two occupants per stateroom for the entire duration of the cruise - only the first and second guest will be charged.
In the case of a Winning Bid in “Aurea” or “Yacht Club” Experience. In these cases, the Guests will also be guaranteed all the benefits relative to the new experience. All services that have been purchased and / or prepaid before the Winning Bid event for an upgrade in "Aurea" or "Yacht Club" experience will not be refunded if the same service, of the same or higher quality, is included in the new experience resulting from the Winning Bid.