Import laws, whats the go nowadays?

Alright, I know this has probably be asked time and time again.. But I can't find any threads that are recent. And therefore, the information may not be correct. 
I have looked into the costs of importing an MR2 turbo from Japan. Now, I know that importing SW20's is or possibly WAS illegal in the past.. But at the moment, I'm having a really hard time actually finding some solid answers! I've searched all over the Australian Government; Department of Infrastructure and Transport website, and haven't been able to find any reason as to why SW20's cannot be imported? 
Previously, I was under the impression that there was a 15 year 'rule', so to speak.. That meant you couldn't import cars more than 15 years old, unless being imported as a 'classic/historic/collectors car'. But, have found no evidence of that restriction? When searching for how I would apply for the correct documents, the site asks; if the car was build, off the assembly line, BEFORE January 1st 1989 or AFTER January 1st 1989. After selecting the second option, it asks if I personally exported the vehicle and would like to import it back to Australia. After selecting 'no' it then asks, whether or not I have owned the vehicle for a period of more than 12 months. After selecting 'no' again.. It then takes me to a short list, three different options.. Saying that I MAY be eligible to apply to import a vehicle under; 'Letter of Compliance Option', 'Discretionary Approvals' or 'Registered Automotive Workshop Scheme'. 

Does anyone have any solids answers? I know it's a stretch, because I see no reason as the why the laws would have changed.. But, without any solid evidence.. I tend to doubt what is or isn't factual! 

Yep exactly what Worldwalker said.
 
15 year rule is no more, it's either pre Jan '89 rule, or SEVS (specialist and enthuiast vehicle register).
The only other rule is a personal import rule, which is where if you are an Australian citizen whom lives overseas, if you bought a car while you were there and have proof you owned it for at least 12 months whilst living permanently overseas, you are eligible to import that car back into Australia, regardless whether it is on SEVS or not. The car still has to be able to comply with ADR's though in order to be registered.
 
There are also restrictions on how many vehicles you are allowed to import under SEVS, I believe no more than one car in an 18 month period.
http://www.infrastructure.gov.au/vehicles/imports/index.aspx
 
SEVS register
http://rvcs-prodweb.dot.gov.au/sevs/sevsindex.htm

going through the list... you can bring in an Ariel Atom!!

But what a fun way to stay regular . . .