Speaking from experience, working overseas isn't necessarily because Australia isn't great, but rather, it's an opportunity to be in a different market and prove your agility in adapting. Some countries/markets are more developed than ours and we can learn from them, whilst others are a bit behind and there is opportunity for us to share our insights and experience to help them in their development. Nothing is absolute but ultimately it's the ability to operate in each of these different markets which proves your ability to adapt to changing situations - and that is something which is both personally rewarding/satisfying, as well as a trait which makes you that much more employable or valuable in the future.
(ps. I say this after working in three different countries besides Australia - all with the same employer)