i can answer that to what i have experienced.
i do not buy optics ready guns.....however...
i have sold some of my guns, and the first thing the dealer says is, "well it's NOT optics ready, and nearly everyone wants such a used gun, and frankly, i cannot give you a high offer".....
that does not stop me from selling one of my non-optic guns, as "we haggle" and i do "ok" in getting a good price.
same thing when i sell a gun that has factory iron sights, not night sites.....
i do not buy night sites.....BUT, if a gun i buy happens to have them...ok...i guess.
there isn't much $$$ difference in an optics ready gun over a non-optics gun, and many times, when on sale, i get what i like, not what everyone else says different to.