OK....
CAMS - Confederation of Australian MotorSport - http://www.cams.com.au/ (you need to be a financial member of a CAMS affiliated club to get a CAMS license).
AASA - Australian AutoSport Alliance - http://australianautosportalliance.com/aasa/
If a day is run under CAMS insurance - you will need a CAMS license.
If a day is run under AASA insurance - you can use either a CAMS or AASA license.
Phillip Island - will ALWAYS be run with CAMS insurance, so you will 100% need a CAMS license to compete in any track day at Phillip Island.
Winton - it depends on the club running the day and whether they take out CAMS or AASA Insurance, most of the time people who run days at Winton use AASA (coz its cheaper), but its not always guarenteed. Steve, you'll need to check the supp regs for the day you want to enter to check if AASA is acceptable or not.
DECA - the same as for Winton. When SAU Vic run a DECA day we use AASA as our insurance provider. But as this day isnt one of ours, im not 100% sure which insurance the WRX Club will use. You should check with their motorsport committee.
My suggestion - if you guys are going to be doing a day at PI, you will need CAMS anyways, so you may as well just get that.
2 years in a row now we have bought 10 plus track cars (also to note there were some of the quickest track cars in Melb) up to Sydney over Melbourne Cup Week, doing track days at Wakefield and Eastern Creek both times. All cars have driven home both times without any issues.
Mexico is civilised - of course you can get parts. You think we get all ours shipped down from Sydney
Steve-O - if you need help getting any of the above info, just holler
Bec