I broadly share the views of Sue Allan in her post of 03nov 11 07pm.
I think songs and tunes were composed by all levels of society from the humblest to the higher echelons.
They moved in all directions and were picked up by performers who took a fancy to them.
Some of the material remained much as the original and others changed to the taste of the performer or his audience.
With regard to the quality of the songs,a farm worker could easily have had a better use of words than a bad broadside writer or vice versa.
The argument as to who had the most influence depends on the the opinion of the commentator,whose views will be shaped by what he or she thinks is most important.
No one today knows exactly what happened in the past,the only evidence we have is snapshots of the time,what the collectors chose to record.
What they chose to leave out of their collections and the explanatory notes.