Caveat: I am currently based in India but have traveled extensively around the globe during my corporate life (before I turned fultime GMAT tutor). This includes Australia, Europe, and the US of A. This is based on my experience in the corporate world and not as an MBA Admissions consultant
Firstly, Melbourne Business School is a good place and you will see that though few alumni have made it big in US/Europe they are still densely concentrated in Australia/APAC. At the end of the day success post-MBA depends largely on where your network is concentrated. It is not so much in other countries so that kind of slims your chances.
Secondly, from a "perception" basis the fact is that in the US, even a mid-tier US school outweighs a Melbourne Business School. This is primarily because companies feel they are more equipped to understand that American way of doing business. Europe is not radically different.
Finally, a lot depends on your post-MBA sector, which you have not mentioned here. There are some sectors in which MBS might be strong - and some in which it might be weak. I would recommend using Linkedin to see where the alum group is spread. Perhaps it would be a wise idea to reach out to some of them and solicit advice.
Hope this helps,
Arun
