There is a tremendous advantage to having two eyes instead of just one. (Close one eye, and go jogging through a forest.)
I agree. I am rather attached to both of my eyes.
I can't think of any advanced critters that have only one eye, so my guess is that the selection of this (two eyes) trait goes back quite a long way in the evolutionary chain..... much earlier than the development of skulls, for sure.
How did two identical organs evolve independently from 'a single patch of light sensitive skin'?
The same question could be asked about having two lungs, two kidneys, two arms, two legs, etc.
If the evolution of these structures originated as a localized (not originating in the brain or in the nervous system but due to a slight alteration in the form of a small area, such as the skin, of the organism) and gradually appearing event, how came about the exact same thing twice?
Answer: it didn't.
This is especially obvious when we consider that organs such as eyes and MANY others are said to have evolved over and over again INDEPENDENTLY of one another.