not moving into higher income areas just because you can,

At least in the US, the biggest reason for moving into a higher-income area is because the quality of public schools tends to track the median income ( and schools are funded mainly through local property taxes).

If you are already taking --step 0. Do not have children--, then that can probably save you more money than several of these other steps combined. But it's not really helpful advice for the people that do decide to have children.