The case for an Australian Republic can be couched in many different ways depending on the audience and the format. It also depends on the response you are trying to elicit. That is, the case can be made in a campaign, like in 1999, in which a Yes vote is the desired response, or an out-of-campaign period in which the speaker is seeking active support of a more general kind.
"Persuading Australians to actively support a Republic,"
ADR Bulletin: Vol. 10
, Article 3.
Available at: http://epublications.bond.edu.au/adr/vol10/iss1/3