Listen to Liam O'Flynn playing it. Plenty of ornamentation but also plenty of beautiful clarity. He's solo first time through but is then joined by some fairly dreamy harmony (that I think works well, but hey ho). I think that ornamentation overload comes mostly from the heaviness with which the ornamentation is played rather than the amount of it. There's the abandonment of the notion of steady rhythm which requires great skill and understanding - in the wrong hands (including mine) it can sound self-regarding and, at the extreme, just pulls the melody line to bits. No easy answers with slow airs!