The consequences of failing to pay a ticket are entirely dependent on circumstances and luck (or bad luck). If this was an auto-generated ticket such as from a camera, the citation is necessarily linked to the registration not the driver. If the car was a rental, the default fine will wend its way back to you through the rental company, along with what can be very substantial costs associated with the process which all get tacked on by the company. If the car belonged to somebody else, the default fine will wend its way back to the registered owner and the reg will either be suspended or not renewed when the time comes.

If this was an "in-person" citation and does not contain the vehicle reg. info., it's unlikely to track it's way back to you, but in unlucky situations it can. Not likely than anybody is ever going to arrest you and ship you back to Australia (I think that "transportation" as a penalty ended back in the 1980's), but information occasioanlly wends its way back through all manner of bizarre databases, not necessarily law enforcement. When that happens, the unlucky find themselves with higher auto insurance rates, unable to rent cars, occasional credit hits and the like.

You have to be genuinely unlucky to get caught up in this, but only youc an judge whether it's worth paying up and being done with it or finding yourself in the middle of nowhere 6 years from now and being denied a car rental at some out-of-the-way airport.

Incidentally, you never know what might come of sending a letter first asking that the issuing authority take pity. No nastiness, no silly legalese and the entire thing fitting on one page with a photocopy of the citation attached and a prepaid international mailer (avail. at the Post Office) enclosed. Worst that can happen is nothing and you can then pay or not pay as your own conscience and the practical considerations above dictate.

Oh, and don't forget. Don't go back to Australia ! Whether or not your physical driver's license in the USA is revoked, your right to operate in Australia will be revoked and that's a much more serious issue.