I remember playing on one of the ferries in The Great Ferry Race (part of the Festival of Sydney) when the James Craig was brought into the Harbour to be restored; great sight!

I've no real idea of your "particular interests" and I've mentioned only the landscape, as I suspect that, visually, that's what will be really different from Maine. The Prom might be a bit far away in the time you indicated you'd be in and around Melbourne, and is worth a weekend at least, so a shorter (and more doable) trip might be down the Mornington Peninsula to Flinders and Portsea. Things have changed since I courted in the area but seeing the Heads (the entrance to Port Phillip Bay) is worth a trip. Of course you could also see them from the other (western) side, on the Bellarine Peninsula but that side of the Bay is different.

Good travelling!

Cheers, Rowan