Thanks for all the advice. I have decided to get a PPL.
So far I'm 5 hours into doing a full PPL here in Australia, in a C172N. The gap is the theory exams and 2 hours of instrument flying, and of course learning how to fly a heavier aircraft and passing the flight test, which will mean doing some cross country again to get the standard right. I think that I could do the whole conversion for 10 hours if all keeps going well, but I will just keep going till I'm done. It's good to have refresher training anyway.
I'm loving it. My 230 hours of sport flying are helping a lot and get recognised, so in reality once I am to the right standard I will be okay.
Once I am complete I will apply to the FAA to convert it then visit the USA to get checked out to actually be able to use it over there.