Perhaps, but you might learn more in CA; bigger market, moves faster, more experienced co-workers, stronger culture of entrepreneurship, generally bigger thinkers.

Worst case scenario is that after earning USD for 2 years on an E3 visa, you return home more experienced than your peers with "Silicon Valley Startup Experience" in your resume, if that is something that appeals to you. Stronger startup ecosystem on the small scale, bigger problem sets on the large scale.

Don't get me wrong, the startup and tech scene in Sydney has grown into a solid network over the last 5 years, but you have to weigh that against the certain knowledge the Bay Area accounts for 40% of U.S. venture funding and even that pales in comparison to the tech giants who are either based or have sizable offices here.

In terms of lifestyle, Sydney will always win. I suspect this is why there is such a strong loop back home after Aussies spending some time here.