After thirty years of house prices rising astronomically, you can't appeal to "speculation" any more. People are speculating because the underlying scarcity makes prices sure to rise.
I think if you look closely at "population down, house prices up" you will find normal supply-and-demand stories like "population down, houses down even more" or "population down (downtown), prices up (suburbs)".
I think if you look closely at "population down, house prices up" you will find normal supply-and-demand stories like "population down, houses down even more" or "population down (downtown), prices up (suburbs)".