Well, I can't say I know any of this first hand, but there ARE some good winereies around Melbourne. Though most at least an hour+ drive out of the city, so it'll be a good thirst/appetite inducing ride. Could be done though, but I'm not clear on bike routes out of the city. As someone mentioned, there's probably a bike route map available for this.
On a side note, the regional freeways do permit bikes, since they're less traffic laden, and are a great smooth ride, just watch out for the occasional road trains (i.e., huge double-rig trucks) that are probably the most dangerous vehicles to cyclists on the freeway. Or if you want even less traffic, more countryside, the older back roads along the freeways are ideal, though narrower, a longer ride, and slightly less smooth riding.
For an alternative to travelling out of Melbourne, and if you want to get to the surrounding smaller cities/towns, the V-Line train services (the regional train network) are usually very good about bringing your bikes on to the train. As long as you keep it out of the way, i.e., not obstructing the doors/passge and prefereably avoid the peak services (7-9 am arriving at Melbourne, and 4-6pm LEAVING Melbourne), you'll have no trouble. So if you want to leave the city and base yourself out of town for a few days, the train can bring you to a regional centre like Ballarat, Traralgon, etc, from where you can cycle to surrounding country towns, or visit the local wineries at your leisure.
http://www.vline.com.au
I'm no expert on wine regions, or wineries, but I do know there are some good ones around. You probably have seen this site in your Googling efforts, but
http://www.visitvictoria.com/displayObject.cfm?objectid=89283F2E-24EB-4610-B28393DCDB470957 is quite informative.
Sorry for the rambling post, hope that was helpful. I really should learn to compose my thoughts properly.
