As long as we keep telling the bogans that Melbourne is the world's most liveable city and they keep believing it then Melbourne remains the world's most liveable city.
I've never had a problem using SkyBus (or other airport bus services) so don't believe a rail link will improve anything. SkyBus runs every 15m in peak, and other companies e.g. the Dandenong Airporter, have reasonable timetables if you are willing to book beforehand.
Melbourne metropolitan trains still operate with a steam age mentality. Nearly empty regional services are given higher priority causing delays and blockages in the city loop to regular metropolitan trains, and when these regional trains eventually pass they get every red signal at every station along their way to the country. And if a normal train is cancelled along a line at peak hour then all subsequent trains are full like sardine cans. You would think the train company would be able to shunt a train or two travelling in the opposite to peak to pick up the fat just like the trammies do so well, but no its all too hard for the sh!t for brains running the system.
Honestly, I don't want or need a rail link to Melbourne airport as it will be crap just like the rest of Melbourne's rail network.