"Wasn't one of the root causes of Japan's decline a property value collapse?"

The root cause was Japan's lower interest rates which resulted in borrowing money in order to lend money at higher interest rate. [An interest rate is suppose to reflect risk and account for any future inflation]. It is true that the bulk of this glut of money was used to buy real estate.
You could say that with the lower Japanese interest rates, US real estate [or other countries with their higher interest rates] with higher interests rates were "seemingly" dirt cheap [maybe, you could say that Japanese investors were ahead of the times:].