If you're singing a long ballad, I think it's important to remember that you're telling a story. If you sing in a way people can't understand, you'll lose them - and rightfully so. Also, I think that audiences have less tolerance for hearing long, long songs multiple times. The story maybe be teriffic the first time around, but not if you just heard it last week.
John McCutcheon's Christmas in the Trennches is a terrific song - but I'm sure I like hearing it at every McCutcheon concert I attend (I've been to a dozen, I think). Same goes for novelty songs - they wear thin if sung too often.
Oh, if you want to hear ballads sung as if the singer were telling a story, take a listen to Judy Cook.
-Joe Offer-