Honestly, you can probably walk up to Sushi on 5 whenever you want and if the Maitre d is around, negotiate a good discount. Not sure how good the vouchers were but especially on the Panama Canal cruise, the place is so quiet as to nearly look abandoned. Keep watching for the FV on the Panama Canal sailing as those cabins are awesome for that itinerary, maybe they haven't released them to smaller parties yet. I did a bid from an inside and got one on ours.