I thought that Sydney Wildlife World was tiny but extremely classy with the design of many of the exhibits. Huge viewing windows and fairly naturalistic environments are the norm within this building.
The whole idea of Widlife World was for visiting businessmen who didn't have time during the day to go to the zoo, to be able to go to this place at night and see the aussie wildlife - originally it was open until 10pm.
Ans it's a good idea - when I was at Taronga there would often be people visiting the zoo for less than 45 minutes. They'd tell the guides they want to see "a kangaroo and a koala". They'd usually get to see some wallabies, platypus, echidnas, emus and wombats too.