2. Why would she return to her previous level? It's said that becoming such an energy being is the highest level for the Ocampa. Why would she, as the only Ocampa dislike that paradise-like environment so much that she had to return to a pervious level?
I certainly share your frustration with this episode, but characters evolving to a higher plane is almost no better than death: writers paint themselves into a corner. I'm not surprised, for instance, that Wesley Crusher's dialogue was expunged from Nemesis as it would raise so many questions about why he would return to run the menial nightshift on the Titan in Nemesis. And if Sisko's return from the Celestial Temple had been depicted in the series, I would find it laughable if he took up again as a Starfleet officer. (Although it might make sense if he went back to cleaning clams.) Addressing Kes' return needed to be, in some sense, spectacular.
Now, I don't like to correct people's writing, and I hope you don't take this the wrong way, but I laughed at the idea of Kes returning to her "pervier" self.