We always buy Memory Maker at WDW and come home with hundreds of pictures. Love it, love it. When we went to DL last year, I didn't think twice about purchasing the Photopass+ because that's just what I do ... While I'm glad that I did (and I've already ordered it for our DL trip this September), just know that you're not going to come home with NEAR as many pictures as you do at WDW. I felt like the characters at DL are out in more places and more easily accessible at DL than at WDW, but very few of them had a photopass photographer. I usually had to have a cast member snap a picture with my camera. And there aren't as many photopass photographers just out and about either - we had a 4 day hopper and each day when we were at DCA, I tried to get a good picture of us with the Mickey wheel in the background. I found a photographer there only one time during four days! There was consistently a photographer in front of the Carsland sign. So .... with that being said, you're going to feel like the pre-purchase of $70 is a steal since we're in the habit of dropping $169 at WDW, and I think it's great to have those pictures as a back-up in case I lost the pictures off my camera. Just know that you're not going to run into as many photopass photographers as you do at WDW! (There were photographers at the character meals - Ariel at the entrance of Ariel's Grotto, Goofy at the entrance of Goofy's Kitchen).
