Texture and tasty morsels
I agree that texture is an important aspect of nymph design. Sandy did some really neat stuff in that regard.
But I was referring specifically to foam and dry flies. Last summer, when I was tying and fishing flies that were tied on straight pins rather than hooks, a good number of fish would take the fly off the surface and retreat to the bottom holding onto the fly. A number of times a fish would hold onto the fly until I physically pulled the fly away from the fish. The most dramatic example was one fish that was big enough and held on tight enough that he broke off a 5X tippet when I tried to pull the fly away from him ( although it is possible that the straight pin got lodged somehow that he couldn't release the fly, but he still must have been a pretty good size fish to break the tippet ).
Those flies were FEB flies that consisted of furled antron, foam, deer hair and rubber legs tied on a pin that was only as long as the forward body of the fly and fully encased by all that soft material. There was virtually nothing hard for the fish to feel, only the stiffness of the pin. The fishies, not all of them but a good number, were holding on to, not spitting out, the soft materials. That was the effect / result of a lot of texture in the flies, to my way of thinking.
The fish are always right.