"Goodnight and God be With You" is a Lowland song - all early sources for it from there, and Scott thought it related to the Armstrongs of Northumbria. I doubt many Highlanders would think it one of their own.

Irish, Scottish and English tunes are all heterogeneous with many overlaps every which way. There isn't any single national characteristic for any of them. If you can find Alois Fleischmann's "Sources of Irish Traditional Music" it does a good job of showing just how complicated the influences are, even when you confine yourself to printed sources.