I wasn't able to see the opera, and of course the opera has never been a repertory item -- it's mostly Fleming (and before her the Slovak soprano Benackova) who have gained it a little foothold in the last couple of decades.
But the music is continuously beautiful (as generally with Dvorak), the story of the soulless nature spirit who wants to become human is one of the central European myths, and I'm always glad of a chance to see it. (The chance doesn't come along that often.)
Yes, Fleming is probably past the peak. That still leaves her in good shape.