There just isn't that much to do in my opinion. Anything I have in mind for you to do, you could most likely do in Sydney. Since you'll be coming in summer, the beach is always nice.
Here's a good link for upcoming events in Melbourne:
http://www.thatsmelbourne.com.au/inf...&pg=2191&li=82
lollerskates @ asian food festival.
There's 522 events to shuffle through, at the top right is a search field where you can choose to limit the search to a particular period of time. It's probably best to use that method to get through everything.