My wife [aka the Finance Minister] will tell you that it is not really viable in terms of return on investment. None of the species that we have imported, or will in the future, can be sold in this country.
However, they do boost visitation. Year on year that has been the case so far. We are certainly not the prettiest zoo in Australia but visitors are impressed with the diversity of our collection and also that we encourage all of our staff to "have a chat". They don't expect to come to a zoo that has so many different species [many of which they don't get to see in today's homogenised collections]. They also don't expect to hear about our many conservation activities - especially with species that they don't get to actually see - Greater Bilbies comes to mind here.
Thus, the visitation income driven by the diversity of our collection, finances the conservation side of things.
Couple this with keeper talks that don't lecture our visitors and you pretty well have our Business Plan in a nutshell.
On the personal side it gives us some satisfaction to be able to support some of the better run Species Management Programs as well to boost low populations of some non-managed species in Australian zoos and even to restore some species that have already been lost here. Watch this space for more along those lines.