Eric: The fish may indeed not see them from underneath, but in order for the fish get under your fly, the fish needs to see it coming.

I don't necessarliy want my mayfly imitation to "surprise" a trout as I would say, a hopper or beetle. I want the fish to see it ahead in it's feeding lane.

I feel a trout may ignore your fly at the last moment, but will rarely elect to eat it on a whim. Rather, I feel most show they are interested far before the fly is directly overhead. This is where I feel wings are critical as they appear to a fish well ahead of the body or footprint. During a hatch I just do not think trout "suddenly" eat anything.

That said, "how" wings are imitated is up for discussion and may blur the line between angling and tying a bit. I like upright divided wings on my hackled flies, but there is no arguing the effectiveness of Flick's Variants.