I've also sung Scots songs, from similar sources as above, for 45 years. I first learned from MacColl (live and on LP) and then went to Scotland and learned there were better Scots accents!

To me, the accent and meter is essential to the meaning in many songs - both comic and narrative. It helps to carry the meaning. But whether to drift in and out of gae/go or noo/now is far less important. Songs often do that, themselves, (use both forms in different verses) depending of what a regional singer has added. As I "process" songs, I tend to drift in the direction of "ballad Scots" since I was first familiar with that. That works fine in Scotland - everyone can handle ballad Scots but there are hundreds of regional words & phrases that are not genrerally understood.

I'm not really good at accents but I tried hard...I feel I do "well enough" as my Edinburgh friends (and Arthur Argo) generally said I sang with no accent at all. That is, they couldn't hear any particular NuYawkese from me but no particular Scots, either. I took that as a high compliment. (I'd thought I was "ach"ing & "brr"ing all over the place but apparently not...seems I was basically singing BBC Scots.)

For me, the key is to actually understand the song. To gloss it fully before even learning it. I think that will automatically reduce idiotic Mondegreens - both sung and as heard by the audience.

Fact is, I percieve a different problem. It's easier for me to sing a Scottish song (I sing well over 100 of them) to an auditor fully familiar with the genre than to a Florida group. In Florida I constantly have to deal with the problem of the song being understood. I sing 83% for the value of the text (of course, it counts that I'm a poor singer and sing a capella) so if the story or joke fails, my listeners might just as well be hearing a Chinese cat in a wine press.

I have to deal with the old problem of rendering a song from a foreign language into the standard vernacular. Some do this brilliantly - partly because they understand what they're singing, partly because they are fine performers. But I have to decide whether to fully Anglicize, to Anglicize text but retain accent and some obvious words (eg, gae, when in context), to split the difference (like singing a repeated refrain first one way, then the other) or to try to explain the song first.

(Of course, if I'm singing one of those English country amorous songs, I'm inclined to first let on it's bawdy so that won't get lost.)

I don't think there's a "correct" answer to this - depends on the audience, the specific song and the skill of the singer to convey just what s/he intends to convey.

Here's a question: What accent should be used to sing "The American Stranger?"