For me, this question is quite simple because I do not write my own songs. I don't think I could ever evaluate my own material objectively anyway. But I do believe I can spot the folk performer who has got just the right combination of vocal performance, instrumental ability and songwriting skill to make you just perk right up. I either cry, laugh or am amazed at what I hear. Then I go out and listen to all their stuff and inevitably choose some of the best, at least that's what people tell me.
And because many of these folksingers are not well known, it may as well have been original as far as the audience is concerned. It gives me quite the variation in style for my repertoire and unfortunately many folks who insist mostly on their own originals inevitably become boring as the performance progresses.
This is a tough call. To make it in any real way, you need originals but most of us will be mediocre and probably better off doing someone else's best songs. Think about some of your favorite folkies and how many of their songs you wouldn't do and then think about what percentage of YOUR originals are worth hearing. Not being driven by any creative juices, I made my decision to be as effective on stage as possible some time ago.