Serious question: how much of that alleged $700k/year-to-mothball is real, hard cash NASA has to spend, vs accounting formalities like "how much would the site be worth if put to its highest and best use" (and taken as a paper loss because the site isn't being used)? Or one-time costs that were incurred for mothballing, but aren't likely to be repeated annually (like shuttering the building, building a fence around it, etc)?
Don't discount the accounting formalities. I once worked for a company where upper management directed us to immediately dispose of about 100 non-obsolete laptops... at a disposal cost of more than $900 apiece. Why? Because they were sitting in a stack in the middle of a mostly-empty datacenter literally covering most of a square block, and some idiot in the accounting department decided that they were costing us $25,000/year to maintain for no reason besides "they're taking up 100 square feet, and we're paying $250/foot per year in rent"... in a building that was about 95% empty & leased for 20 years at the height of the dotcom boom just because "it was there". The fact that even if you take the fictional annual rent for the floorspace seriously, it took more than FIVE YEARS just to break even on the insane disposal fees. And in the meantime, we had to buy new laptops to replace the ones we were ordered to dispose of, because new people were still getting hired. Wait, it gets better. As a matter of policy, we were required to ship the laptops to the disposal center via FedEx. Priority Overnight. Individually. Almost a decade later, I *still* can't grasp how anybody could have possibly thought it was sane, let alone a *good* idea.