Personally I'm a fan of the Union Jack, it's own history, and the history we inherit by carrying it. It's where we as a country have come from and an identity I would personally not like to forfeit.
But Australia has long had its own history and identity separate from that of the UK. We're all not Anglos 
. As an Australian-born with mixed ancestries but who sees himself as Australian and only Australian, the Union Jack means nothing to me other than it's a flag of a foreign country.
Furthermore, it's modern historical revisionism to claim the Union Jack is on our flag for "heritage" reasons (I know this is now taught in schools 
but it doesn't make it any less baseless and simply untrue). The Union Jack is there because it had to be when the flag was first created. No non-British ensign design would've been allowed to win the 1901 flag competition. Our current flag is simply a blue British ensign with stars added as local symbols (i.e. 'defaced') as was required within the British Empire back then. Britain was our superior and we were subservient to Britain, which is what the Union Jack in the canton represents (a standard rule in vexillology). All colonies/dominions of the British Empire were required to have one of these 'defaced' British ensign flags (mainly to identify where merchant ships came from). Canada, India, South Africa, NZ, Kenya, etc ... (a quarter of the land mass of the Earth) all had a 'defaced' British ensign flag too but virtually all have since changed their flag to one of their own.
In 2015, the British Empire is no more and long gone and Australia has, over the past 114 years, systematically separated itself from Britian (the 1986 Australia Act officially made the UK a foreign country to us). We are no longer ruled over by a foreign country, so the Union Jack should go from our flag's canton and from our flag full stop.
Blood has been spilled and victories have been won for that flag. There will be no tradition if it is just thrown out every generation or two. If the flag is changed I'm sure in another 50 years we will raise the question again because it doesn't mean anything to so many of us that haven't seen it fly for anything meaningful. Take the anthem for example. The majority who want it changed are those who remember singing God Save Our Queen at school. Then there are those of us who have known nothing more than Advance Australia Fair and consider the thought of changing it sacrilege. Sure I'm Anglo (actually more Saxon than Anglo but still) and I couldn't really give a stuff what ethnicity someone has descended from, what Australia considers the UK as or what any other country has done, to me it is a very important part of where this country has come from.
Traditions are changed and new ones created all the time. Old ones become irrelevant and newer relevant ones come into existence in their place. It use to be tradition to forbid sport being played on Anzac Day or to work on a Sunday. The tradition of the annual Boxing Day Test at the 'G only began in 1980, whereas the tradition of the Australia Day test at the Adelaide Oval has gone by the wayside with the A-League taking its place to create a new Aussie Soccer tradition. As you mentioned dwaino, we've changed our national anthem to our own unique Australian one, despite blood being spilled and victories won under 'God Save the King/Queen' for 80 years (make that almost 200 years if you include our colonial history as well).
A nation evolves, changes and progresses. It takes and incorporates ideas and institutions inherited from older as well as contemporary civilisations and then adds its own ideas, hence creating and developing its own unique identity and culture over time.
Britain's history is itself a perfect illustration of this process. It traces ideas and institutions right back to Roman times where they inherited written language in Latin script, the rule of law that underpins weatern society, cities including London, York and Bath, roads and other key infrastructure, Christianity, art, architecture, maths and science from antiquity, etc. The modern roots of the British people come from Germanic barbarian migrations and French (Norman) conquest/influences from which the English language, culture, government & executive evolved. The Renaissance from continental Europe (mainly Italy) brought with it a rebirth of science which enabled the development of much improved ship-building and navigating technology for exploration and conquest of distant lands beyond the local seas that would become the British Empire. Yet, despite coming from all this foreign heritage and tradition over millenia, there's no S.P.Q.R., no old Germanic, no Norman-French, nor any other flag in the canton of the Union Jack for "heritage" reasons. Instead, from these inherited sources, Britain and its people evolved into a nation with its own unique sense of identity, culture, nationhood and their own independent flag.
Australia and us Australians have gone through the same nationhood evolutionary process incorporating inherited, borrowed and our very own ideas:
* After the Eureka stockade, near-universal male suffrage and the secret ballot was introduced in Victoria (and before the UK did).
* Female suffrage in Australia also pre-dates that of the UK.
* Upon Federation - the Senate, state upper houses and the name of the federal lower house borrowed ideas and names from the USA. We're a federated state unlike the UK.
* The hellfire of Gallipoli and the massive death and casualty toll of WWI from carnage and disease/illness gave birth to a separate Australian identity. My dad's side of the family certainly switched from being monarchists to republicans thanks to WWI (a great uncle died in the war).
* It took until 1930 to gain our own Aussie governor-general despite opposition and disapproval from King George V and the British parliament.
* It took until 1942 post-Federation before we were no longer answerable to the British parliament via the Statute of Westminster.
* In WWII, the USA came to our military aid when Britain didn't/couldn't/wouldn't.
* In 1966, the introduction of decimal currency meant a switch to the American terminology of dollars and cents which replaced the old pound, shilling and pence.
* It took until 1967 before indigenous Australians were recognised as citizens in their own country.
* In the late 1960s, for the first time, Britain didn't fight alongside us in a major conflict (Vietnam).
* It took until 1972 until the White Australia policy was fully abolished.
* It took until 1984 before we had our own unique national anthem.
* It took until 1986 before the Act of Australia separated our legal processes totally from the UK and as a consequence the UK became a foreign country under Australian law.
* Demographically, we have changed significantly over the past century. The majority of Aussies now no longer come from the UK. All of us make Australia what it is today.
From all this unique Australian history has grown our very own unique sense of identity, culture and nationhood.
And there's two final pieces of our evolutionary process to go:
(i) having our own Aussie head of state.
(ii) having our own flag which no longer (and wrongly) says we're still a subordinate colony/dominion of some other country in the 21st century.
