Would concurr with previous comments on exchange risk/exchange costs.
I'm based in sydney and when I convert euros into AUD,I pay 1.1% margin on exchange mid rate + the hassle of organising transfer between Ireland/Australia.
If you are going to reconvert when u get back to Ireland is another 1.1% which means u need to clear 2.2% after tax of your Australian deposit account over Irish account excluding exchange risk.
Its' a no brainer,if u intend to go back to Ireland after your visit to Oz,then leave your money in Ireland especially with the ECB increasing rates this year which should add further strength to euro.