Part of this is that the AUD has appreciated in value so much over the last few years
Yep, many other countries have had economic downturns lately, a lot of australian economy is based off mining, which is going OK. Ergo, currency appreciates.
Part of the problem is retail rental rates are so high
DANGER WILL ROBINSON! That's partially a sign that the property market is in a bubble or inflated. Many other countries have been wrecked when the property bubble pops. It might happen in Australia.