Oh, I completely disagree with your assessment of the original Uhura, Davejames - you might want to rewatch some TOS if you haven't recently. The original Uhura came across as an intelligent professional with a great deal of personal dignity. Mind you, this was mostly because of Nichelle Nichols, not the way the character was written, but it was definitely there, and that's in spite of some "girly" lines. I don't think you're giving her nearly enough credit.
I like the new Uhura, too, but I don't think we would have had a new Uhura if the original hadn't managed to be a compelling character.
^ I recently rewatched a TOS episode ...of course i can't remember which one at the moment, where Kirk was snapping at Uhura to make contact with someone on the planet (it might have been Operation: Annihilate), and she had been trying and couldnt make contact. She looked at him with steely eyes and told him in no uncertain terms that she had tried and couldnt. Major balls in that moment. She was no girly girl!
And she was definitely the same Uhura that told Spock that she was serving on the Enterprise (as in the NuTrek movie).
QFT.
Granted, the original Uhura was very underwritten, as well as inconsistently written - thus lame 'girly' lines like "captain, I'm frightened". But watch "Mirror Mirror" and see that she was no girly girl by any means. This is a woman who doesnt take $hit from anyone (look at the scene in which MirrorSulu hits on her), and who can fight with guys if needed. Another great moment is in "The Naked Time" when she answers swashbuckling Sulu's "I'll protect you, fair maiden" with "Sorry, neither!"

And as JustKate says, she always came off as a professional with a lot of dignity, her colleagues and superior treated with respect and had confidence in her professional abilities (see her scene with Spock in "Who Mourns for Adonais") and she was not scared of talking back to Kirk or Spock (the above scene that Yeoman mentions, the scene in WMFA I mentioned above). A lot of it was probably not so much due to the script, as to Nichelle Nichols - she did indeed have a commanding presence, and that steely gaze she could give people. For instance, in "The Squire of Gothos", they gave her no lines in the scene when Trelane is talking about her and the yeoman (they are both supposed to just stand there) even when Trelane makes a racist remark - but she does her best to make up for it by shooting a deadly glare at him.
And it was nice that "Bread and Circuses" that she was the one who figured out what it was all about. So, no, although we did not learn too much about her, she did not seem vacuous.
I am a huge fan of Uhura, and of Nichols, but I think you are seeing the past through revisionist eyes. You mentioned Mirror, Mirror -- Uhura also almost repeated her "I'm frightened" line ---Kirk then had to reassure her that she could distract Sulu on the bridge.
I think that you are giving Nichols too much credit for having clout on the series. From what I understand, she was paid weekly and was not under contract. She may have been sleeping with The Big Bird, but in many cases Uhura was underwritten or poorly written. I have also read that she frequently mangled/forgot her lines and directors always needed to do many reshoots for her.
Never mind her ever-evolving story about how MLK encouraged her to stay on Trek...first it was a phone call, then she met him in person, etc. This story has been retold and expanded by Nichols in nauseating fashion for years...who knows the truth, but I honestly doubt whether she ever had any contact with MLK about staying on Trek.
Nichols, Takei, and Koenig view the past through revisionist lens...they were bit players on a '60s space opera...to hear them talk about their contributions and their parts you would think they had been the leads in the series!
I love TOS dearly and love all of the actors...but the "supporting players" tend to have a distorted view of the roles they played in the 1960s.