Well I might get flamed, but here goes.
I'd say there are more disadvantages to getting citizenship than advantages, especially if you haven't lived here long.
Citizens do not enjoy any more advantages than PRs. Unless you consider that being forced to be on the Electoral Register is an advantage (voting is compulsory here and you must vote in Fed, state and local elections, well actually you don't have to vote but you must turn up and have your name crossed off the list).
Citizens cannot under any circumstances (or none that I could find) take their Super (pension) overseas or access it in any way before you retire. This may be important if you ever go back, because remember you are forced to commit 9% of your salary to super. They tout it as 'employer' contribution but it's not, when the legislation came in about 10yrs ago, base salaries everywhere effectively dropped, so really it's your own money. It's one of the reasons that wages in the UK can look higher than here.
Once you are a citizen you cannot use your British passport to leave Australia, or enter it as your
PR visa will be invalid, even if you have not applied for an Aussie passport. I found this out to my near peril when going on holiday to NZ. Just received my Oz passport in time.
The only advantage a citizen gets is that some (by no means all) Government jobs require you to be a citizen before you can apply.
There might be more pros/cons on paper but as far as practical day to day living goes that's all I can think of. This of course does not take in the 'emotional' argument, but that would be another question all together.