So, I am going to step into the line of fire and say that I think this is something I would use. Not at BG, but possibly at SW and DC. Many of the animal interactions are hard to capture on film, because guests don't have access to the right vantage points. I'm thinking of things like the Dolphin and Sea Lion feedings at SW, and pretty much everything at DC.
There was one year that we were able to pay for unlimited digital pictures at SW and it was really great. They had taken a ton of pictures of us that we simply couldn't get ourselves (even with our underwater camera). I wouldn't have been interested in prints at all, and I certainly didn't want t buy all of them separately. But I had no problem paying the flat rate and getting all of my pics for the entire day digitally. I was disappointed they discontinued the offer, in fact.
So. Yeah. I think it is a great idea.