This is worth a trip for the people watching alone! We had a blast spotting all the fantastic costumes and got into the spirit with our own. Tickets are affordable ($30 for adults with a free kids ticket with every adult) and include everything inside except for the autograph stations with sci fi celebs.
My advice would be to wait until day 2 so things are mildly quieter, avoid taking a pram is possible and dress up! Public transport is the best way to get there with easy access with trams and trains, otherwise parking at South warf is available.
Warning- there are all sorts of costumes wandering around so if the kids are a bit sensitive it might be best to skip this one.