I recently bought the Danny Lyon book 'The Destruction Of Lower Manhattan'.
Wonderful book in which he documented the old buildings that were being demolished, around 1967. Some of these buildings dated back to the civil war. He writes that at the time he didn't like the effect of modern cars in front of the buildings so he settled on early Sunday mornings as the best time to photograph.
Nevertheless there are still plenty of mid 60s cars in most photos.
I find them to be an interesting element -
they give me a sense of the era in which the photos were taken
interesting contrast between two parts of American history
in a way the cars represent the mentality of mass consumerism that leads to the state of mind that decides to raze 60 acres of beautiful & significant buildings.
I know what the OP means about the ugliness of modern cars - i often used to look at stuff from the 50s by W Eugene Smith, Robert Frank etc & think how lucky they were to have those amazing curvy chromed cars in their shots. But the ugly cars of today will undoubtedly look interesting in 20 years time as people realise how much things have changed.