Sally Garden has a known author-- Wm. Butler Yeats! several people have tried their hands at setting his poetry to music; not sure whose setting I know. I therefore doubt any relationship between Willow Garden and Sally Gardens.

   On Barbara Allen-- I subscribe to John Greenway's belief that it started as an English music-hall song (yes, in the 1660s, once the Restoration had allowed the theaters to reopen) but attributed to the Scots.

Midnight on the Water is also a composed tune-- the great Benny Thomasson. (see the County album "Texas Fiddlers")

gcarrier62-- are your assertions testable? that is, can you point to other gongs in which the allegories are known to be there? if not, I can equally say that the song is a precursor to Gilligan's Island, with a happier ending.