Can I upgrade just one AP in our party from a regular DVC (from last year) to the new Gold DVC (just so I can get the photo pass for our upcoming trip - I'm not willing to pay their full price) What is the upgrade price for this? Thanks in advance!
Yes.
We Upgraded 1 standard DVC AP December to the new Gold pass, even on a Gold "blackout" date, and it unlocked all of that trip's prior Photopass pictures.
It was about a $20 upgrade. (It's really difference between what you paid for the DVC AP and the Gold AP.)
FWIW, it took a lot of convincing the GS CM that They could try the upgrade, but it's just like upgrading a standard AP to the one with Water Parks...something they do regularly.