Grey Imports are bikes that were built for other countries, generally Japan. Even though a bike may have a similar, or the same, name as an official import the internals and electrics can be different. Even a slight variance in a part can cause problems.
If the part isn't stocked by Honda/Suzuki/Kawasaki/Yamaha Australia, you can have a lengthy wait it to come from Japan, they same can be said of low volume or older bikes.
I had a GR650 (don't laugh it was the only 'big' bike I could afford at the time), the bike was sold in Australia by Suzuki in very low numbers, I think the Army bought most of them. Anyway, I had an off at 120 and needed to replace the left foot peg. It took 7 months to get one from Japan.
To be honest, as you live in Melbourne, I don't think you'll have too many problems, as I said before most of the reputable Importers have good stocks of parts for the bikes they sell, some even offer a warranty.
As an insentive to buy from these guys, they often have "Learner Packages". Buy the bike, get a Jacket, Helmet and Gloves thrown in. I think Sumoto do a lot of these deals.
However, beware if you intend to tour as I know a number of Dealers in country areas that won't touch a Grey Import, even in emergencies. This is because they simply won't have the parts for them.
The other thing to think about is that most Grey Imports are not new bikes, they are used bikes from Japan. To make matters worse some of them, particularly the 400's, are ex race bikes or wrecks.
If you haven't already, check out Just Bikes or Australian Motorcycle Trader (AMT) or
http://www.bikepoint.com.au/portal/alias__bikepointau/tabID__0/DesktopDefault.aspxPersonally, I wouldn't touch a Grey Import, but remember I live in country NSW and it's hard enough to get parts for the B12 over the counter. If I lived in Melbourne or Sydney and just wanted a 250 for commuting, then I'd think about it.