So far I've found at least one useful nugget. In "It's not your story", Macris begins by talking about the history and problems with the use of "story" in RPGs, then (in the page linked) he goes into sandbox design with an eye to enabling "emergent story". The key insight here is a way around a creativity-blocker that I suffer from--a sort of "blank page syndrome" and perfectionism. When I think about designing a setting, I worry about making it all fit together from the start, so I'm naturally tempted to use a "top-down" method. What Macris suggests instead is, basically: make up a bunch of cool stuff, scatter it around the map, and then let your mind wander in creating however much interlinkage you want between them. Obviously there's room for revision as well.
There's some similarity between this approach and others that I've seen, but this is at least a reminder that creativity is an iterative process. For reference: The Conflict Web, by Chris Chinn (possibly hard to locate these days); Microcosm, by Levi Kornelsen; the Adventure Funnel, by Dr. Rotwang!
Also compare Rob Conley's excellent sandbox construction articles from Bat In the Attic.