Stone Guards are a 'dress up' cosmetic item that are primarily intended to 'gussy up' a plain-Jane face - much like a woman uses make up to enhance her appearance. No real value, other than enriching the image of the cheapest car made in America. Nothing wrong with that. Some like a 'classy gal', others appreciate the honest plainness of the basic platform.
But like a great many other 'improvements' these accessories were primarily made to make the makers and sellers rich. Secondly to make the buyer happy. No real loser here, only winners.
While I enjoy the 'Up-Scale' look of the Stone Guard on my Deluxe '31 Coupe, I would find the Stone Guard on my '28 Phaeton an obnoxious eye-sore, especially as they were not available in the '20's & '30's.
35 years ago when driving the many miles of dirt and gravel roads in Alaska and Northern British Columbia, I installed a wire mesh screen in front of my '30 Coupe's radiator, and had my original 1930 Stone Guard in front of that. In that case it was not about cosmetics, but about a real need. But I think few of us drive those kinds of roads anymore, and the need is more about our own desires to fulfill our sense of aesthetics.