Japan did not have any major infrastructure investments during the 90s and 00s.
Japan grew rapidly just after WWII.....primarily due to a huge investment programme.
Would be interesting to see if history repeats.
Though I agree the lower population growth will slow things down.
Time will tell.
Sash i think your cause effect links are too remote with regards to Japan and the australian residential property market.
However i noticed you focus on cash flow positive properties and are based in Sydney. So it could be possible for you to find investment opportunities when the time comes (but this wont be because of japan it may be as a result of your location and preference for cash flow positive properties).
Sydney didnt go balastic over the last 10 years (major peak was in 2003 from memory), so the downside shouldnt be as great.
Also you could play the interest rate fixing game: ie buy and then fix interest rates when the rates are low.
This is why its always difficult to provide generic opinions on an asset class.