Alright I'm not sure if those are good examples or not, but here I go!
So first this one, which is a painting by Donato Giancola.
I wrote down the extreme values of bothe the metal and skin. As you can see, they both have the same highlight value, but the skin darkest value is lighter than the metal one. And that darkest value on the skin is really there in very few spots. That's because skin tends to have a much narrower value range than metal since it's less reflective. Also the value changes on skin will tend to be smoother. Also the rock ground is less reflective than both.
As far as texture goes, you can compare the ground which is really textured against the skin which is rendered much more smoothly. And the robot is kind of in between.
Then this one by Fernanda Suarez
The major highlights spots are on the face and the knife, which indicate that they're more reflective than her clothing. And the clothes have a much narrower value range, ranger from dark midtones to dark with no real strong highlights. Then there's various textures of her clothing, like the fur materials which is rendered with smaller and looser brushtrokes for example. I think those variations can really help minimize the plastic you're talking about.
As I said I'm not sure if these are the best examples or if my explanations makes any sense, but I hope this helped. 
