I do think it is high time that the zoo had a proper museum/gallery - the Society has a great collection of art etc and a fascinating story to tell
I wholeheartedly agree with "Pipaluk" that people visit zoos to see live animals and most people wouldn't pay £35 to see a zoo museum. Of course, the living collections must take priority.... people go to the zoo to see live animals.....the living collection has to come first. The general public won't pay £35 to look at a zoo museum and a few animals (no elephants, bears, sealions etc)......
Nevertheless I also agree with "Oflory" that London Zoo has a fascinating story to tell so should have a museum showcasing its history.
The two points of view are not mutually exclusive; there is room for both.