I pretty much agree with what Johnny J said (half a dozen posts in). Just to state my credentials, I started in this game in 1968, singing mostly my own songs. I would always include a couple of trad songs, and maybe a tune or two, for variety and familiarity. My thinking was that not everybody would want to listen to a whole programme of unfamiliar new stuff. I didn't know much in the trad line, but was on the lookout for more, as I loved it, and my own songs were written in a style that would sit comfortably alongside the old stuff. It certainly wasn't navel gazing or 'teenage angst'; I was already an old geezer in my 22nd year! After a couple of years, I ran out of inspiration, and was getting deeper into trad songs, and gradually became a traddy. So it isn't as if I have anything against singer/songwriters. But I do agree that there is too much emphasis on new songs. As has been said above, most songs hit the ground nose first; they always did. A few stay around and keep re-surfacing. Eventually, they get called folk songs. Every generation should be adding to the collective repertoire, but in the long run, it's the public who decide what survives. And it isn't a conscious decision. They just know what appeals to them. What generally seems to work best (unless you are the new Tom Paxton or Ewan McColl) is, as has been suggested, to mix your own songs with trad or established contemporary songs - or blues. This way, people will probably remember more of your stuff than they would otherwise. And some people might be more inclined to come and listen to you than they would if you were only singing your own songs. You get a reputation as a singer of somgs, some of which happen to be your own.
Trust me - I know stuff.
John Kelly.