Went from an IS to the GS for the exact same reason! I have an ultra white, but I have to say, that atomic silver looks pretty nice too!

 

Great car. I'm glad I'm not the only one missing an Fsport badge on the rear!
There's Lexmania in Sydney but that's about it - the scene here is based around 1+2 gen paddock bashers. I've never seen a lowered 4GS or some nice bodywork like on some of the gorgeous vehicles we see on this forum. I spoke to Lexmania and they can order in your Tom's/RR racing type parts if you can work out whether they suit RHD. There's certainly no online mod shops that list any GS parts like the US have.
Not sure about what's in Melbourne but I order all my servicing/genuine parts from the UK to skip the 300% Australian dealer markup, although I'm assuming your vehicle is too new for indy mechanics.