Don't need a study to know rain, sun, and temperature extremes are bad. Let alone bird feces, insects, leaves, rodents, thieves, snow, and meteorites... and in my case, jet exhaust from a nearby airport runway, settles to create a hazy gray film.
Yes it will increase electrical contact oxidation, or rodent gnawing on wires, or UV degrading insulation as well as degrading practically everything the sun shines on. There are many many reasons and items of concern, like UV degrading your tires and headlamp lens, any rubber and plastic trim especially, but at the same time I don't mind if a vehicle that isn't brand new, doesn't look brand new as long as it doesn't look like a**.