They're not gonna get near that amount. YOu forget bureaucratic 'touch/taste' (as in Chicago style). This is just an excuse to piss cash money down the hole to a few "refi organizers" and then to pass on a tax credit to the homeowner that real TAXPAYERS will have to pay. So, in effect it isn't a $75B whammy, it's much much more than that.
BTW, a real TAXPAYER does not get back more $ than he paid in. EIC'ers, AFDC'ers, SSI'ers, SCHIP'ers, and so on.