Squawk. from the amount of security work that has been done, starting last September, the threats have been judged as credible. Some real money has been spent by both State and Federal Governments, and the cooperation between police and the defence force is something to see. I'm not sure what the hourly rate for a Blackhawk is, but they have been using up plenty of hours in the training.
The bit that surprised me last Wednesday was seeing "defence in depth", its not just the F18's, there are layers of defence to stop your hypothetical light aircraft flying into the MCG or anything else going bang somewhere in Melbourne.
It doesn't "matter" if you fly into a packed MCG on Grand Final day because its a purely local matter unless you happen to be a muslim, in which case you are the latest terrorist martyr in the "war on terror", and are hence newsworthy.
Anyway if you did, and only killed Collingwood supporters, no one would care.