Sorry to name-drop guys, but a long time ago I had a conversation at a gig on the Renfrew Ferry in Glasgie with one of the very best (in my not-always-humble opinion) songwriters, Eric Bogle, about this very subject. When I nervously asked for his blessing on my performing his material, he told me that he writes the songs to be performed and that he's happy for anyone to perform them, with two provisos:-

1) Always tell the audience who wrote them.
2) Don't copy his version - do them your own way.

My experience is that writers are, in the main, very generous people (and I've met and 'borrowed' material from some crackin' ones). I think the majority would agree that the sincerest form of flattery is not in imitation, but in loving their songs and giving them air. It doesn't have to be a perfect performance, nor 'Stars-In-Their-Eyes', just one of a song loved and enjoyed by performer and audience alike.