They are a piece of history for sure, and reminds us of much simpler, innocent and desirable times.
Another important part of the Coca Cola advertising is you always recognize it's Americana; it wasn't something overtly done, but done out of who we were as a people. You still feel the sense of who we were and are as Americans, or if you're not an American, who we were, but to a lesser extent today, who we are.
That America has gone, at least for many people, although there is a significant number who cling to what we were and represented at the time.
As far as the art work, it worked well with the characters and props associated with it, while Coco Cola was viewed and included as one of the joys of life that accompanied who we were.