Plato's world view is completely backwards. A good example of the pitfalls of speculative onanism. His influence on occidental culture is still very pervasive, though, but anthropocentrism is as idiotic as geocentrism.
> ... the generally positive connotation of “nature”.
"Nature" is inherently hostile (see Thermodynamics, 2nd law). What's currently marketed as "natural" is a carefully vetted subset, the result of thousands of years of humanity influence on its environment.
As you mention, the definition of the word has been evolving. I think the current meaning is misleading. It causes people to reject man-made things arbitrarily, and, more generally, it perpetuates an anthropocentric view of the world.
Wishing it had (and advocating for) a saner definition is not silly.