Tough to balance. I think a lot depends on why you're performing: to please the crowd or to please yourself (I know, the answer's "Yep.") If you think highly of a song, and your performance of it (regardless of authorship), and you think it says something you want to say, then you should do it. But if no one's listening, what's the point - which is where familiarity is a great tool. Opening with a couple of sure-fire connection numbers puts people in a much more attentive mood for less familiar stuff. I think.