Jill ... The Andrews Sisters used vocal harmony all the way through it, the song CALLS for vocal harmony all the way through it so USE it ... However, when performing you might want to play a song before and/or after using minimal vocal harmony so that you and the audience don't 'tire' of it ...
I would suggest that along with listening to Scott's songs you take a listen to Uncle Dave's at http://www.boydsongs.com/songs.htm
...especially "A Nightingale Sang" ...
t.