your saving rate gets down to zero if you feel your house is already saving for you

Yes, there could be a "wealth effect". But one would expect it to bring down the savings rate, which hasn't happened in France. It is somewhere between 15 and 16%, as it was in 1999 before the boom. There was an uptick in 2001, 2002, then an easing off, but no really significant fall.

In fact, this can fit with my point above: as the grasshoppers spend (because they have made money on the boom), the ants save (because they are faced with a rising barrier of house prices and feel forced to save yet more).

Your demographic point offers an at least partial explanation for increased domestic consumption because the demand for new housing is (still) high and the building industry is at full stretch, creating jobs. (Quand le bâtiment va...) However, if credit doesn't follow, new housing will slow down and construction workers get laid off. From anecdotal local evidence, I know that demand for new housing is stymied by difficult credit conditions, and builders' order-books are emptying.