According to The Star Trek Compendium, NBC's advance publicity for the second season of the original Star Trek promised fans episodes focusing on secondary characters Sulu, Scotty, and Uhura. I have no idea if such spotlights were ever considered, but the fact is that they never made it to air. Uhura remains to this day the least developed of the core Trek cast. She wasn't even granted a first name until J.J. Abrams' 2009 Star Trek film. Notwithstanding the three episodes where she got to sing, "The Lorelei Signal" is the closest thing to the promised spotlight on Uhura that Star Trek ever gave us.
In the Wikipedia entry on this episode, it is stated that Nichelle Nichols considers "The Lorelei Signal" her favorite Star Trek episode. That's certainly understandable, for while its not quite the Uhura spotlight she or fans of her character may have hoped for, it is one of the few episodes in which she got to do more than just sit at her station on the bridge repeating her signature line, "Hailing frequencies open, Captain."
In addition to this episode, writer Margaret Armen worked on three installments of the original series, "The Gamesters of Triskelion", "The Paradise Syndrome," and "The Cloud Minders," none of which are likely to appear on anybody's list of Trek's best episodes. Its not that they're bad, per se, but that in a series capable of such excellence as "City on the Edge of Forever," "Journey to Babel," and "The Menagerie," and others, they're just a little bit disappointing. "The Lorelei Signal" is actually rather mediocre, coming off more like a 1950's B-movie rather than an episode of Star Trek, and would ultimately be utterly forgettable without the Uhura sub-plot.