Lesson 101 about currency exchange. Change your money the least amount of times. So, you will never win if you change AUD to USD, then USD to Rupiah. Doesn't matter how good/bad the currencies are.
About the current situation. There are two reasons the AUD is high against the USD at the moment. Firstly, the USD is failing against most currencies, including the Rupiah and AUD. Amercia is so desperate to try and stimulate their economy they are printing money, which devalues their currency. Secondly, the AUD is stronger in general. If you look at how it is performing against many other currencies such as the Euro and Yen (Japan are also printing money) it shows that the AUD is high. This is mainly because of the relatively high interest rates in Australia at the moment. (and please excuse the extremely simplified explanation to any economists/financial gurus out there)
The Rupiah is also doing ok against many of the world's currencies, so even though the AUD is almost parity with the USD, you are not getting significantly more Rupiah as it is also strong.
Bottom line, take your Australian dollars and change those to Rupiah. If you are in Bali first, you may get a slightly (as in a couple of bucks per 100) exchange than in Lombok. The exchange rate on the Gilis is terrible, so definately change money before going there.
A good place to see roughly the exchange rate is here
http://www.klikbca.com/individual/silver/ind/rates.html, look at the far right hand column, bank notes : Beli (buy)