Work out what you are trying to achieve first by going overseas and be realistic about your expectations. If you are just interested in travelling for a year or two and getting some temporary legal work, then fine but be realistic about the type of work and pay that you will be offered and how it may affect your legal career.
Consider how your work experience will look on your cv when you get back home or you try to find a serious law job with an employer. Your experience gained in those years working and travelling may count for nothing, so you may find yourself actually going backwards not forwards.
What is most important to you? Quality of work, lifestyle, money, reputation. Moving to work outside of Australia will often mean earning considerably more money but that is not always the case and take into account any payments you have to continue making in Australia such as a mortgage and renting out your property.
You may earn less money in another country but your lifestyle may be better and the cost of living may be much cheaper.
What about my current employer - they don't want me to go overseas and tell me I don't need to? Of course your employer will want you to stay. Just ask yourself this how many people in Australia, or even your own employer, do you know who have worked overseas, enjoyed it, earned well and either stayed or come back and continued their legal career in Australia and prospered as a result.
Decide for yourself but it should not be too hard to realize that Australians generally travel well and contribute enormously to overseas businesses.
Your biggest asset will be creating an international network of people with whom you may to continue to work with for many years to come.
Should I specialize or generalize? - Up to you. You will probably find that the most obvious legal markets such as the UK will have large commercial law firms who have very specialist teams and that may suit you while overseas. Keep an open mind and don't expect the same structure that you have in Australia.
Will I have a job when I come home? - Hopefully, but this obviously depends on the market conditions and the work that you did while you were away. If you come back with skills that are in demand then yes the chances should be good. Keep in touch with Australian employers and plan your return home as carefully as you planned your trip overseas.