Hi Jim,
While I totally agree that voice training and working can no doubt improve performance, have you found any evidence amongst the travellers you collected from that they did any sort of exercises or work to achieve the performances they give? Did they just have a natural talent developed from the oral tradition ?
I have lately taken an interest in the Child collection and a friend loaned me a copy of "My Precarious Life in the Public Domain", a CD of Child Ballads by John Jacob Niles. Now there's a singer who definitely did his exercises .Whilst his high voice singing style comes close to opera, he still puts the story across in dramatic fashion. These recordings were made from 1939 to 1942 and are well worth a listen