Basically the optical difference between the original acrylic enamel and BC/CC is one of "depth" - in BC/CC you're of course viewing the color through a layer of clear.
The reason for the BC/CC on modern cars is appearance and protection; it'll stand up to stuff the old enamels won't, and retain a shine longer. Similar logic to panel fit, people aren't as tolerant of the weird gaps that used to be commonplace and were sometimes a warranty hassle. People were simply less demanding 40-50 years ago.
The difference in texture is part inherent in modern chemistry & equipment, and largely in the color-sanding & buffing. If the painter can lay down a very clean finish, and you avoid the 1000/2000 wet-sand & polish (just nib & polish any dirt), you can have some texture.