I see what you are saying.
If you booked the early saver rate the price is guaranteed. So you can call Carnival and get the current price. The decision they will give you is what deck do you want. Since you booked the Riviera deck before, they should let you rebook on the same deck and receive the discount. However, if you want to remain on the Upper deck it sounds like the price is the same. You know....you could possibly move the Main Deck. It should be a discount and it's still an upgrade from the Riviera!
I would suggest you call your Carnival Planner and discuss all the details and see what they can do. I hope this helps!
Enjoy your cruise,