I immediately did the same calculation. It's not that much relative to the footprint of a house, but it's probably quite huge compared to the footprint for an equivalent capacity natural gas or nuclear plant.
Whether it makes sense depends on the potentil revenue generation value of the land -- the opportunity cost. It wouldn't make economic sense in the Santa Clara Valley in CA, where land is fabulously expensive, but it might make sense in an undeveloped area of the Sonoran Desert where land is cheap -- e.g. on the outskirts of the Phoenix area. This discounts any environmental costs, of course, but these also would vary from site to site.
It's pretty clear this is not a technology for solving *all* our energy needs (as nuclear was intended to be in the 50's and 60's). But the nifty thing about electricity is that it doesn't matter where it comes from. You don't have to put all your eggs in one technology basket, you can use a mix of sources. Which means you can stop building these things when the marginal *environmental* cost starts to go up. You just have to build enough to reach economies of scale that allow you to make a decent profit.