The current system rewards you (most of the time) for finding said hidden keys and paths on your way to said "boss". So even if you don't find the "boss" of an area, you can still gain some of the obs/exp xp from the zone. In your system it would again be an all or nothing where there is the possibility of spending a bunch of time and getting nothing if you miss the 1 and only thing that gives the perk for the whole area.