Not sure if this will help you, but I wanted to post how my upgrade was handled last week. We had 4-day MYW hoppers as part of our MYW package. Package was discounted (code was out when we booked); since the TA gave me a total amount, I'm not sure if my tickets were discounted or just the room portion. Anyway, we upgraded to 10 day premium (including the plus pack and non-expiration). They (Pop concierge) didn't look at my info to see how much I paid for my tickets. They had a chart that showed how much each extra day cost, added those together, and added on the $45 for the plusses and the $100 for non-exp. The total upgrade cost me $178 and a few cents! So, in actuality, the extra 6 days themselves were next to nothing; most of the price was the non-exp and the 5 plusses. That will cover a couple more trips.
I just have to make sure I save my room card as that's what the tickets are on. They gave me some printouts w/ numbers in case I lose the cards. If I lose both the printouts and the cards, i am out of luck as that's the only way they can look up the tickets. So I've got to find tow good, safe places that I won't forget about to put everything (they said to keep the cards and printouts separate just in case).