Someone with more Disney experience, please correct me if I am mistaken.
However, I think you would be better off using the 2 days on your old pass and then buying a new hopper for your remaining days. The way I understand it, you can use your old pass to get into the park on a day for day basis (2 days, in your case). However, if you turn in your old pass for a new pass, you are credited $ for $. This will be much less than 2 days entry since prices have increased so much.
Something to consider.