In my opinion only:
In Australia clean unmodified and original cars are hard to come by, however they are not rare cars overall. Stock collectible cars are already increasing in value over more worn/modified models. However, and its a big however, there were 40,000 + R32s made.
The more collectable cars in my "order" would be Race/GrpA/Historically signifigant cars, ADM models, N1, Nismo cars, VSpec II, Vspec, and then the rest.