It has been said before but whilst it is cheaper to import the car yourself,I know that the idea of paying for a car which you cannot see and the actual importation process can be a turn off for many buyers.
Also, I think it'll take a car enthusiast or rather, a skyline enthusiast to fork out $30-$35k for a r34 (average price for one which has been landed/compiled and sold privately or through dealer). Most models ive seen on sale at this price are 98 and 99 and whilst they are still in great condition to us, the fact that it is fast approaching 6-7 years old may not be so appealing to an everyday buyer who wants a car to get from A -> B
Alot of the younger buyers wants a r34 but they simply cant have one because they cannot afford (buying/maintaining) the car
Ii think that the new p plater restrictions will also affect the number of r34's on the road
This leaves the more mature crowd where speed is not number 1 on their agenda.. As such, they usually turn to newer cars due to warranty and lower maintanence costs.
I dont think we've reached the stage where there are too many r34's in Australia yet. I can go through a week and see maybe just 1 or 2. Maybe in a few more years, we will see as many r34s as r33s thus causing the price to decrease even more.