Our country may have a strong economy, but, we are still too weak to become a republic and there is no way known that we would be able to get the power the US has attained.
In times of war (i.e. now) it would be the worst time to break our monarchy with England (We don't even have a nuclear arsenal!!!). We are also in a global economic crisis. Also it may just be me but the thought of Kevin Rudd being our president would scare the crap out of me (Mr Big spender). I am a liberal follower as the state of the economy that John Howard gave us was great and I really wish that he was still in power (John Howard as president would be ok).
But no us being a republic would take the prize for our nation's mistakes.