Depends on how much you value those pictures.
If you are the sort who would shell out for attraction pictures (like Splash Mountain, Space Mountain and others), then it can quickly become a value. Also, if you are doing a lot of meet and greets, it also is a nice feature to have.
However, if you don't plan on doing those things, save the money and just ask the Photopass photographers to use your camera (they will) to take the shots you want.