I agree with Ray Ring that Dayton Duncan and Ken Burns are on to something with the idea that public lands and "resources" ought to be reserved for the public and not allowed to be a source of enrichment for private individuals (HCN, 9/14 & 9/28/09). This theme recurs throughout the "Best Idea" episodes, along with a variety of other pretty good ideas, such as the notion that parkland management should focus on maintaining the sort of iconic wildlife (wolves, grizzlies and herds of large native herbivores) that do not long exist once lands are diverted to private ownership.
In the West, it's no secret that there is a tension between advocates for a variety of public-land concerns (wilderness, roadless areas, wildlife, native fisheries) and people who believe that the "public domain" is best used by being privatized. To me, Burns/Duncan's "best idea" is the understated but explicit concept that transferring public lands to private individuals or firms (through ownership or contract, lease or permit) so that a few people can divert the natural riches of the public lands to their own private pockets is not good for the country and its people. Our maturity as a society will no doubt be recognized by future historians in our willingness to prevent the diversion of ever more scarce public lands to private gain. This ever-evolving notion of stewardship for our public lands is really our best idea.