Reading the manual online I've found you can turn the screen off by hitting the "option" button near the iDrive controller and scrolling to "turn screen off" (or similar- it says something like that).
Not sure if turning it off means it also folds up though. I'd hope so, won't want it up if I'm not using it...
Just have the nav on normal 3d, but set the scale to 175 or less. Then go and drive up to a cathedral or something. Stuff like stonehenge are tiny but recognisable. Stadiums etc look good.