I suppose, technically, a hotel does not OWE a guest anything above and beyond what the guest is paying for, even if the guest's room has been upgraded. In other words, the guest is not ENTITLED to more than what the guest reserved and is paying for.

However, it seems the guest should be able to enjoy all attributes of an upgraded room. For example, lounge access is a published feature of a Concierge room on a Concierge Floor. To deny lounge access to a guest who has been upgraded to such a room seems petty and insulting. It makes as much sense as upgrading a guest to a balcony room, but then forbidding the guest from opening the balcony door.

Room rates are another matter.