I always found that it is best to arrive at your interpretation when you are researching the song (in preparation to sing it). If you are lucky you will find something fresh to hold your attention every time you perform it ( a bit like reading The Good soldier Svejk).
This is particularly true of ballads which always strike me as being fairly unequivocal in their intention. This does not mean that you can't continue to discover nuances in them; but the general meaning is usually quite clear.
One exception was MacColl's re-interpretation of the ballad The Bonny Earl of Murray, which he reckoned he had misunderstood completely in his early days. His later re-interpretation changed it from a lament into a scathingly ironic piece. He wrote a fascinating article on it in one of the folk magazines.
Jim Carroll