You can't help that happening, can you? It's like the second time you hear a joke and you know what the punch line is going to be, it's never quite the same. And the emotional effect a performance has on you also varies with the state you're in at the time, too.

By the way, performing an "art song" isn't exactly the same every time either.

In my experience a performance does settle down over time, but then there are random "experiments" that occur on the spur of the moment, and there are gradual changes which you notice if you listen to something you recorded a year ago and think - golly, I don't do it like that/so fast/slow etc now!

"do other people who are interested in traditional song,feel that interpretation should be spontaneous,and should differ from rendition to rendition..."

Erm, excuse me, but what is this word "should" ?
Looks a bit prescriptive to me.

Anahata