I've attached an article in Bloomberg about coupe values. Carl Nelson talks about coupes are beginning to increase in value.
http://www.bloomberg.com/news/articles/2015-02-24/why-you-should-invest-in-a-vintage-bmw-3-0-coupe
http://www.bloomberg.com/news/articles/2015-02-24/why-you-should-invest-in-a-vintage-bmw-3-0-coupe