The most solid argument in this direction (IMHO) is that quite a lot of the extra spending seems to have gone on positional goods, like housing. It's mostly a bidding war, and once every family has two earners, the winning bid is much higher.

And, making that worse: Once you have two careers to plan for, it's much harder to move to a smaller cheaper city to escape. Perhaps both of you can find good jobs in the big city, and in 5 smaller places... but not the same 5! So you have to pick the big center.