AOPA and the others will first get "duchessed" - wined, dined and fawned over.. If that doesnt work the department will try divide and rule eg. "we like talking to you RAA, you are so reasonable compared to AOPA".
You will be sucked into discussions of detail; eg. "what do you precisely mean by "benefit to the Australian economy" Mr. Morgan?".
You need to find a good constitutional lawyer to assist you, preferably someone who has worked in PM&C and knows how to write Acts. You need to go in with a set of principles to be enshrined in the Act and make bloody sure they get in there. You have to get the black letter law right and accept no assurances or you will be screwed every which way as in; "well Mr. X may have promised you that but he retired last week and i have no knowledge, etc. etc."
My 2 cents: FAA plain English rules, separate regulation and enforcement, remove criminal penalties and strict liability and of course foster the industry or at least be prevented from killing it.
Then of course the charade of getting it tabled and voted and passed which is another hurdle.
Good luck, the odds are stacked against you.