Short of historic or "special" attractions (Yellow Stone, et al), I believe it should be sold off. Preferably slowly, but not "centuries" slow.
Respectfully to the NPS employees here, your agency's brass has collectively lost its friggin mind. They love stealing land, for either zip or pennies on the dollar. Only time they offer market values is if the owner is connected, or spends years in court. I'm less than thrilled that they used a UH-60 to play mall ninja games... That's pretty friggin low.
Personally, I'd say let the GAO do a study on what to sell off and how do to so, then have the GSA handle the selling part.