Brawny has a good point about the inner and outer. But i can visually tell when i have finished my flys, my mid chest has that fiber look to it and much more pumped than not having done them.
Upper and lower forsure can be targeted. I used to only perform flat and decline benching, after cutting declines for incline i noticed a big difference in bringing up my upper chest. Especially when the inclines are dumbbells
We lift weights and manipulate our diets so that we'll look good naked. Sure, it's healthy too, and we'll probably live a longer and more productive life than the average guy, but mostly it's about the naked thing.