"I don't really want once again to take over Richie's thread "
One of the problems with this Steve, is you still discuss these ballads as if you know the printed versions are the originals when you in fact have no evidence that this is the fact - you've just done so on the Scarborough Fair thread regarding Lucy Broadwood's note on herb lore.
I have no interest in defending Buchan's behaviour, but I do know that the jury is still very much out on whether he was any worse than any of his contemporaries.
I don't believe 'authenticity' was too great an issue in the first half of the 19th century, and as you say, they were all at it - I can't see there is that much evidence that Buchan was worse that anybody else (why on earth should Mtherwell, Jameison and Scott "regret" what they did and why should Buchan have to "show regret"?).
Of all the pros and antis on the Buchan CONTROVERSY (which is still the case) -I tend to go along with Keith's argument on authenticity - but I certainly haven't read enough on the subject to be definitive about it.
Huntdsvet makes a number of important points as well, but it's a long time since I've dipped into what he had to say (he may have changed his mind since!!!)
What I do know is that I'm the proud possessor of a very nice early set of Buchan's Scottish Ballads - many of which are highly singable without too much adaptation, which is a damn sight more than I can say about the shelves of Roxborough, Ebsworth and Bagford that are also part of our collection.   
As I can't stress enough - the Buchan enigma remains just that until somebody comes up with something different (like an efficient Ouija board maybe)   
As far as folk song origins are concerned, I wait in anticipation for proof that the chicken came before the egg, or vise versa - but while they are treated by people in these discussions as done-and-dusted, they remain an issue with me.
Jim Carroll