It's usually the unusual I find that sells well everywhere.
I bought a mixed lot at auction one time and it had an old zippo lighter in amongst it. To be honest, I was going to throw it because I couldn't see any value in it, but decided to test market it anyway. Ended up getting just over 45 dollars, and purchased from a member in the US.
That's the item that convinced me to always allow international shipping on easy to ship items, and while I've had my eye out for old lighters ever since, I haven't yet stumbled across anymore unfortunately lol.
It does make me smile when I see everyone wanting to sell PS3 or Ipods lol. No doubt in my mind, if you can find collectibles to sell on ebay, then you will get bids from all over the planet, and stand to make a lot more on that single item, than selling 100 Ipods with their margin.
I have a good friend who uses the same sources as you, as do I of course Thrift shops, yard sales, weekend markets and auctions mostly. he finds some really old and unusual things, but for some reason will only list for local pick-up, and strangely enough still does ok. I can only imagine how much better he would do if he was to offer shipping to not only Australia, but international as I do, but I can't convince him of that for some reason.
My theory, if it can be shipped hassle free, then why not. High ebay membership in Australia, and it sounds like you have the right kind of stock to ship. I would see no reason not to offer shipping to Australia, all it can do is increase your chances of a sale by increasing your potential customer base, and that's a key element to ongoing success in any sales field.