I carry UK/AU passports and confirm all the opinions that it's useful to be able to pick and choose which to use. Plenty of countries make life easier if you have one or other.
Two tips:
1. You're already a UK citizen if your father was born there, even if you were born in Oz... or, at least, that's how it was 20 years ago. Having the passport merely confirms the citizenship. Good logic, and as soon as it was pointed out, I went and applied for a UK passport.
2. if you're in the UK and close to a passport office, it's much easier to renew a UK passport there than in Oz, especially if your UK passport is old/expired. In fact, if you're within cooee of Head Office in Newport Wales (and it's a good excuse for a day trip to see Roman ruins) then consider using the emergency renewal process. It costs, but it's over the counter, completed same day, and may well be cheaper than the normal process in Australia. Just ensure that you have made an official appointment and aren't late.
Slightly OT: Mrs TheMaiz has Oz/US and I have Oz/UK passports. Wherever we are, we head for whichever lines are shortest and apply to at least one of us. There's never been a problem even though our surnames are different.