Does
Disneyland not work the same way as WDW for upgrading? I thought they did?
If they do...then you want to ENTER the park with your discounted ticket BEFORE you upgrade. Then your ticket becomes encoded with the CURRENT gate price and you'll get credit for that amount. I've done this loads of times at WDW....if you have an AP then with their free dining you have to purchase at least a 1 day ticket (ok, I think this year it's a minimum of 2 days)...so we always have a 1 day ticket the following year to upgrade to our next AP. But by using the ticket to enter we get the raised ticket price...in other words, we purchased it at the old rate, but every summer they raise the rates and by using it first we get the new year's rate as a direct credit towards the cost of the AP. Of course, it's kinda offset by the fact that the AP goes up every year too, but it's better than nothing.
I know the conventional wisdom is to buy the 10 day hopper no expiration at undercovertourist.com who usually has the largest discount (it's currently about $37).....use that ticket to enter, and then upgrade it to the AP and they give you the full value of the ticket, so you get a $37 discount on an AP (AP's are never discounted, except for military and DVC).