Good point. I think most of us are influenced by all sorts of things, but the influences are usually subconcious when we are actually writing.
Two songwriters who stick out for me are Ray Davies - of the Kinks - and Bob Dylan. They both wrote types of song which seemed very new at the time. In the case of Ray Davies, he quickly progressed from the normal teenage pop/rock love song to a more quirky, observational style. He wrote some delightful character sketches -"Mr.Pleasant", "Sunny Afternoon" etc, which were all mixed up with influences from folk songs, rock and even music hall styles. There is a unique ability there to get across serious irony with a big smile.
With regard to Bob Dylan, I am on the side of the true believers. He recognised the opportunity to use the popular music of his time to present serious, complex character studies of his characters. He had the talent to do this well and the perception to realise that there was an audience ready for it. It is hard to imagine songs such as "Ballad of a Thin Man" or "It's Alright Ma - I'm Only Bleeding" before the mid sixties or without the brilliance of Dylan. I know that plenty of folks can do without those songs, but they certainly enriched my life and showed me just how sophisticated songwriting can be as a craft.