"I will try to make sure I add that these are only my own opinions, and the opinions of Child and others."
Fine, Steve - as long as you are prepared to present the full picture.

"Gruntvig
His published collections are, taken together, and compared with the contributions of any single collector, the richest source in this branch of folk-lore out of all that up to this day have appeared before the British public. . . .
That Mr. Buchan has not published his ballads with that scrupulous accuracy, that strict and verbal adherence to the popular tradition, as might be wished, and which may now be demanded, we are ready to confess ; but he certainly has done no worse in that respect than all the ballad editors of England and Scotland, with the exceptions of Mr. Ritson, Mr. Jamieson, and perhaps one or two more. His merits in preservation of the old Scottish folk-lore are so great, that he certainly ought to be treated in a less slighting manner than has been the case . . .
Arguing for the publication of Buchan's MSS., Gruntvig went on
There are reasons to suppose the published versions to be in some respects less authentic and genuine than are the MSS. from which they were taken ; these Mr. Buchan has kept close to the form in which they were taken down from oral tradition; but in publishing them himself he has no doubt taken some liberties with them to make them more suitable to the taste of the day."

"Keith
The late Professor Child, who has been cited by some of the accusers of Buchan as their most redoubtable ally, took up, in reality, an intermediate attitude. Careful examination of Child's work reveals that he never committed himself to a condemnation of Buchan, although he constantly condemned passages in Buchan's ballads which he considered modern importations or examples of decadence and vulgar fancy. Gruntvig's attitude, and the testimony of independent Aberdeenshire ballad versions procured from unpublished MSS., were sufficient to make a discerning and cautious critic like Child pause before he rejected Buchan's contributions. Child did more than pause. By inference at least he accepted Buchan as substantially reliable, and gave him the place of honour with a frequency denied to most of the other great collectors. Child, however, as late as 1891 was under the impression that the British Museum MSS. were all in Buchan's handwriting, and he did not live to see the MS. from which the 1828 Ballads were selected. Had he been able to compare the Ballads with their MS. originals, and had he been spared to see the collection made by Greig, it may be confidently asserted that the prince of ballad-editors would have been on the side of Peter Buchan."

We should not forget that Buchan's contemporaries in the field of ballad scolarship (far more in the position to judge than we are) supported his work absolutely.
Nor should we forget that Child was one of those 'foolish people' who differentiated between 'broadside dunghills' and the genuine songs of the people.
I am not claiming to be right on this question - I, like you, don't know the answer to the Buchan enigma, just as I don't know which, (if any) of our ballads and songs originated on the broadside presses.
What I am saying is that giving the impression that we DO know by delivering definative statements is neither helpful nor honest.
And I certainly believe that one of our most important ballad collections (see above) is worth far more than a bit of a larf!
Jim Carroll