Just copy what the Americans do, they have this process down to a fine art.
Super Bowl tickets, for example, are tightly controlled with the vast majority being keep for the teams to distribute (something like 70-80% split between them), with the rest only being available to very, very, high end corporate partners of the NFL it's self and friends and family of people involved in the NFL, and of all those tickets only a tiny minority will hit the open market (maybe 5-10% if you're lucky).
In other words the way the NFL and others do it isn't realistic in the Australian context (we're just too small, but if you make the event big enough it could work in the future), but the way the WWE does it, mixed in with some of the other elements from the others, would be a great way to go about it.
Bidding for Superbowls happens years in advance, 5 or so give or take, at which point the league and the local government have 5 or so years to market the shit out of it. WrestleMania's bidding process is just as long, however they only announce the winning bid on WrestleMania night a year beforehand. This is where we steal from the NFL, as having five years to market and sell all the tickets would be better for us than one year, however everything else we nick from the WWE.
They treat WrestleMania as a massive event and consistently promote it, slowly building to a crescendo the closer it gets to the event. There almost isn't a WWE broadcast that doesn't mention WrestleMania.
They create custom branding for each WrestleMania that is reflective of the host city, and used it to make each one feel unique, i.e. a once in a lifetime event that will not be repeated, you can go to a WrestleMania again, but you can never go to this WrestleMania again.
They then take that custom branding and fold it into a giant marketing campaign, with lots of cross promotion, to make sure that everybody knows that WrestleMania is coming to town because people can't go down the street or turn on their TV/computer without being bombarded with it.
Once it gets closer to the actual event they make all their wrestlers available to any and all major media outlets to promote it (local, national, and even international on occasion), and invest in, and host, events in the lead up to WrestleMania night that they use both to make an extra buck and to promote WrestleMania.
I could go on, but I'm sure you get the point.
As long as NRL are willing to invest the resources and put in the effort they'll be rewarded.
Just like the Super Bowl, or WrestleMania, as time goes by, and competition for hosting rights get more heated the minimum standards have got higher and higher.
So you might start out with ovals being able to host the GF, but that wouldn't last long as long the GF's are successful events. Pretty soon you'd see a requirement for a rectangular stadium with x-amount of seats, among other requirements that people probably wouldn't even think of, like x-amount of hotels within x-amount of distance, x-amount of car parking within walking distance, etc, etc.