There isn't a list anywhere that tells you what got update. For North America its worth getting the 2009.1 my house built in 2006 didn't have the road leading to it till the 2009 version. The Navi is just but a toy, nice to have your home address show up though. I have a benz E350 also I had to dig around for 4 months to fine the updated DVD.
No idea about the Australia DVD though. After you download just do a sanity check that the structure of the DVD is similar to the one you already have in your car.