You get out what you put in. And the single highest value factor, for me, was the fellow students; my seminars were routinely nearly 50:50 male/female, with folks from a dozen different disciplines, from a half-dozen different nationalities, yet with just enough in common to provoke a productive dialogue and working session. Average age skewed older; most people had careers of some kind already, or were adjuncting or tenure-track.
Update/disclosure: Currently writing my Masters thesis, was at the Saas-Fee location for seminars in 2014-2015.