The other major issues are whether the song is traditional (not a need for a long introduction, for the most part,) or original (may need a longer introduction if it is a story song that needs a setting.) Not all original songs need a lengthy introduction, but some do.

I don't think there's a "right" or "wrong" to this whole issue. The length of the introduction is determined by the audience and their interest, and the individual song, not by a discussion on mudcat, no matter how interesting. Cripple Creek doesn't need a long introduction, while The Battle of New Orleans does. If you're performing at an outdoor arts festival with a roaming audience, neither of them do.