My DW and I have done it on maybe 80% of our trips. We had a short 3 day trip where we didn't by the PhotoCD. The others have all yielded at least 750 pictures and edits, up to about 4750 pictures and edits. Probably 40+ cds from all the trips, just the two of us. Now of those, I think we have printed maybe 80 pictures for scrap booking/framing. But I also have a digital picture frame on my desk that cycles through 400-500 pictures. That is the real value for me.
If you want multiple shots, and something with character of both of you, you will most likely end up benefiting from getting at least the PhotoCD. Yes, the Photopass CMs will take a picture with your camera, but more often than not its 3-5 of theirs, then one of yours. So most of the fun and creative shots tend to come from their camera. The same also applies for character photos. They start snapping away as soon as you walk up, and tend to get pictures with more personality and character in them, whereas the handlers (using your camera if you ask) will often just get the "Everybody smile!" pose. But if you don't do characters, then that's not as big a plus. I suggest looking at what you would end up using the pictures for, as well as how many you would want and go from there.
