The requirement that flight instructors must operate under an AOC. In the USA, most flying training is by highly experienced instructors – quite often older, more mature pilots – who operate independently without the high cost of an AOC.
I'm not sure that "most" flying training in the USA is by independent instructors and the downside is the higher number of hours that the FAA requires for their students compared to those of an approved school. Still, it seems to work well with "older, more mature pilots" called upon as FAA Safety Counsellors and involved in their WINGS programs etc.
Merging the bottom end of GA with RAA type ops would seem to be part of the answer.
On the hardware side:
There's a requirement for an "export airworthiness approval" per section 7.1
http://casa.gov.au/rules/1998casr/021/021c22.pdf
Some relaxation of this should be considered. A part from the USA with a PMA comes with a release certificate from the manufacturer. If I order a part for my aeroplane I also need a Form 8130.
One example at
B&C- an oil filter adaptor for uncertified aircraft sells for $395. I don't have a problem in them recovering the extra costs for the PMA'd one at $450 (exactly same part, they just ask whether you want the extra bit of paper when it is delivered). I have a problem when they say it is for Australia so needs yet another bit of paper and the extra cost just pays for some-one to visit their factory and sign it - for an extra $100.