Just to clarify, Photopass is the service itself. They have photographers throughout the parks to take pictures. You can then buy the pictures at the parks, or at home online. Simply walk up to the photographer, they will take your picture and load the pics onto a Magic band or PP card. You don't need to buy the pictures, you can buy 1, buy a dozen, or make assorted products like Mugs and Mousepads through their website. If you go to claim the pictures online, the Magic band pictures get automatically loaded to your account. Any magic band associated with your reservation will get their pictures loaded. You can also add additional Magic band by typing in the 12 digit code found on the band. If you don't have bands, you can add as many PP cards as you want to your account by entering the number found on those.
Two popular products are the Photopass Archive CD (Used to be the PhotoCD) and Photopass+. The Archive CD includes a digital copy of every picture in your Photopass account online. So any from Magic bands, any from PP cards, etc that you have added along with any edits you do will be on the CD. Photopass+ includes the Archive CD, and a special PP+ card that you can use to claim your dining and attraction photos.
Some people are reporting being able to claim dining pictures with normal PP cards recently, this happened about the same time they stopped giving the physical prints at dining locations with a PP+ card. So now the real differentiation seems to be the attraction photos. This may change in the future once they roll out "Magical Memories", reported to be video clips, but the timeline on that is unknown.
For a 2 day trip buying the Archive CD or PP+ seems a bit much. But as mentioned, they will take pictures with your camera, and you can buy single copies through Photopass of the ones they took if you want.