Several years ago I looked at a potential port upgrade, and the price was no different than it would have been to change in advance. We were a party of two, which might be important. From my understanding, the primary price savings comes from not having the number of guests taken into account, which helps if you have 4 in your stateroom, but not if you only have two.
Very often, no concierge upgrades are available at all, and not uncommonly no upgrades of any kind, even when you're among the first to arrive.