Graemsay, what would be the approx yield on these properties 10yrs from now if the prices will be 80-90% of todays value? What makes you think investors won't jump in before and push prices higher?
Assuming that rents track wages, over a decade they'd increase by around 50%. So the increase in yield would be:
1.5 / 0.8 = 1.875 ~ 85% to 90%
I'd expect things to shift from something like 4% rental yield / 7% capital gains to 7% yield / 4% gains.
If there is a bit slump in prices then the economy is likely to be screwed up, people will be out of work, and the banks won't be lending. And investors with a heavily negative geared portfolio probably won't be able to borrow to take advantage of this so easily.
However I suspect that there will be people who do very, very well out of it.
That said, it depends on how the market plays out. My calculations are based on a consistent, steady growth rate.
Following the 1989 peak in the UK, prices dropped for seven years, with the nadir being in 1996. They picked up during the late nineties, went ballistic around 2000, before peaking again in autumn 2007. This trend is a U shape.
If the Australian market follows that trajectory, then the bottom of the market would be somewhere around 2017 or 2018, prices could still be 30% or more lower by 2020, and possibly more that double what they are now in 2030. Though the whole cycle could be longer.
Secondly, what would be the average wage and approx. disposable income available to service debt? If you think disposable income to service debt will be higher in 10yrs time what makes you think ppl will not spend that extra money to buy a bigger better location house thus by pushing house prices higher?
If prices in Sydney halved then buying a median house would still put a family on a median income into mortgage stress. I don't know about other markets, but I suspect that Melbourne is similar.
Buyers are going to need a growth in income to be able to afford current levels, and I can't see prices rising ahead of earnings over the next 10 to 20 years as other posters.