Fascinating thread - so many thoughts spring to mind reading it. Bev & Jerrys point is so good, and is better than the one I use 'the music has to be in your fingers, not your head'
My daughter has been brought up with folk, has a music degree, and that really helps with learning tunes. eg in sessions 'Whats that tune?' she'll jot the name down, start playing it at home as soon as she finds the dots and will then play it out after a week or so when it's in her fingers. Incidentally, she plays mainly recorder and I'd like some people who think it's second best to a tin whistle to hear her belting out reels or caressing a slow air, but thats off the subject.
Playing for dance is just so important for trad tunes, and an ability to play technically demanding music as classical musicians do does not necessarily give them the ability to keep a strict tempo.
Anyone recall the wonderful programmes with Menuhin playing alongside Grapelli, and some Shetland fiddlers (Tom Anderson?)
I just wish I'd learned to play much earlier in life, and then I might have some idea about what it's like to play classical.