Yes, it's gotten a bit cooler — but don't be so quick to write off outdoor activities completely. There are some that are quite suited to the cooler temps. Take, for example, the Rutherglen Winery Walkabout — it's the oldest wine festival in Victoria and it's been running since 1974. It will be trotting into the Victorian country town again this year, when almost 20 wineries will get involved in a weekend of wine tastings, music, tours and general hijinks.
Before you ask, yes, there's a shuttle bus service to take you from winery to winery, as well as a regional bus to get you to Rutherglen from a nearby regional town. So you and your mates can plan a weekend that doesn't involve someone being a designated driver (and does involve lots of shiraz). There's also a wine check-in system so you don't have to lug around the bottles you buy all day.
You can buy tickets for the Saturday or Sunday or just lock-in the whole weekend with a two-day pass. Tickets for the shuttle cost extra, and if you do volunteer to be the Dave, you'll get into the festival for free.
With too much going on around the place to tick everything off, make sure you plan ahead — check out the event guide here to make sure you know where and when exactly you're going to line your stomach (maybe start with an egg and bacon roll at John Gehrig Wines).