Mate
Don't fly into an airport that requires an ASIC if you don't have one. You don't want the terror police dragging you kicking and screaming from your aircraft. You can find which airports are "security controled" on CASA's website.
It also depends what you're going to do with your licence. If you want to fly to places like Canberra or Ballina you will need the ASIC. If you're flying out of Bankstown I think you'll find you need the ASIC. Also,the AVID is valid for 5 years.The ASIC only 2. More $$$ to keep the ASIC currrent.