Sorry Helen, but there's no way I can see the word "spruce" ever be used in a sense of other than being "smart" in a dress sense. "Smart arsed" of course I can understand but nothing to do with "spruce" no matter how one can try to convolute it.
I have read and been involved in Scottish poetry and literature for a very long, long time and have never come across an instant where spruce can be construed as smart arsed.
As I said I asked the only person alive who might know the answer to our question, Ronnie Browne, the other half of the Corries and you have read his reply.