Robert,
The word superfluous is a good one; gimmick is another when it comes to modern double greens. Actually where I think they work is where space is a necessity, and only where the holes are coming from opposite directions. I've seen Bob Cupp's triple green at The Vineyard, and while he was really constrained with that property, a triple green was both really gimmicky and didn't work. At the same complex, John Fought has a double green with a separating bunker in between. It works, but its really gimmicky. (so therefore, doesn't work in my opinion)
Where I have actually seen it work is at Ocean Dunes in Florence, Oregon, a course I've played probably 20 times if not more. I can only think of a few times I actually was on the green at the same times as another group going the opposite direction--and that shouldn't be the criteria--but in terms of space, it might become just that.