A few weeks ago I took 3 of my friends through "A New Invasion" stealth style. It was two rangers and two rogues, no casters or healers. Only my toon was equipped with Green Steel and raid-loot, two of the toons were my friend's first toons and we all know how those usually turn out. We snuck our way past everything, it was a hell of a lot of fun and maybe killed 10 mobs before we got to the boss. It was an interesting change of pace, like Hunt for Red October" in hell.
The Stealth Mechanics do work in higher level content, it's just really SLLLLOOOOOWWWW. When you're looking for XP or loot who has time for this stuff? My first toon was really gimpy so I learned this because it was the only way she could stay alive, once you build better toons it's just not needed.
Funny thing is we use stealth in epics all the time . . .