"The tunes are also being currently played in some very wierd styles, often of a sort of "pan-Celtic" type with no connection to any known tradition."

Welsh dance tunes are conventional Western music. They are in 6/8, 4/4, 3/4 etc, use familiar scales and were played on familiar instruments such as harp, flute, and violin.

How wierd can that get? How many "known traditions" could there have been?

I say if people want to bring the old melodies back to life, good for them. Many Welsh tunes are delightful and deserve our love.