Hi Josh,
Great to see another SW owner in SA. We've become few and far between these days.
As Rick said, the MR2 scene isn't particularly huge here, but we still exist.
I spend a bit of time in the hills, and travel between Gawler in Mt Barker regularly, so maybe I'll run into you sometime.
In terms of upgrades, I'd suggest leaving it as it is for a while and just get used to how it handles. They're a difficult chassis at the best of times and it takes a lot to master them. I'm still coming to terms with mine after a year owning my GT-S, and I had a 91 N/A for 2 years previously.
Stock Gen 3 chassis have all the upgrades than the Gen 1's and some 2's needed, being the reinforced sway-bar mounts, better suspension and much improved ABS (if you have it). They're a well built car and honestly don't need a great deal of money spent to make them an excellent car to drive.
If you want to upgrade anything, start with your tyres.
A good set of tyres makes all the difference to any car, and you'll definitely notice it.
There's no point getting coilovers, sway bars, bigger turbos, running higher boost or E85 if you don't have traction in the first place.
The only modifications my car has are Whiteline Sway-Bars, and intake and exhaust. The engine, while built, is still running stock boost and timing, and won't need to be touched for a while yet.
You will definitely wear out rears faster than your fronts, I can guarantee that. I've chewed through so many rear pairs in the last 3 years it isn't funny. Admittedly, I drive my cars like I stole them, which certainly doesn't help with tyre longevity.
As Rick said, there's a practice day at Mallala on April 30th that I think most of the SA guys will be going to. I'm also aiming to be there on April 9th and May the 2nd for a private day, but obviously there's no pressure to drive.
I do greatly encourage you learn the limits of your car on the track over driving in the hills. Many people learn the hard way that public roads are more dangerous than you think.
Look forward to seeing you at the track or out in the hills sometime!