So you've concluded that she didn't have a crush on him, based on the evidence... that she acted flirty with him?
I've also concluded that McCoy didn't have a crush on him either even though he teased him about having a teddy bear. I've also concluded that Kirk didn't have a crush on him even when he teased him about "irritation". And the entire bridge teased him, and had fun at his expense at the end of Galileo Seven ... but the entire bridge were not necessarily flirting with him and probably they all did not have a crush on him either.
Yes, I concluded that, too, when Kirk sung that song to Spock about his "devil ears and devil eyes" that drive men on the ship insane, and when McCoy asked Spock to tell him he was a handsome man and talk to him about romantic evenings on Vulcan... oh wait.
And BTW... that "Vulcan has no moon" scene is another obvious example of Spock showing emotions while trying hard not to show them. First he's obviously uncomfortable (
tucking at his collar) before he takes an opportunity to shut down the conversation with the "Vulcan has no moon" line. Then when she (apparently already somewhat annoyed) starts berating him for his lack of emotional reaction to the crewman's death, he gets obviously angry and snaps at her. Just look at the grumpy expression on his face.
Do you think Spock has the socials skills to "shut down a conversation"? In that scene, what Uhura says about the moon totally goes over Spock's head. He has NO IDEA what she alluding to -- and it is humorous. I think she knows this and has fun at his expense again. And this is an element of TOS, and Spock, that the writers of nuTrek dropped the ball on. Vulcan has no moon, they don't flirt, they don't romance eachother -- they don't have our entire gigantic culture surrounding dating, sex, marriage and romance. There was so much room for humor here. Spock is kind of innocent and confused about human emotions and the culture surrounding them. There is a charm in this, lots of room for humor, and it gives us that outsider's perspective from which we could see ourselves. Romance - very illogical but we humans thrive on it.
Spock is innocent and confused about human emotions and culture?! We're talking about a guy who grew up with a Human mother who showed emotions all the time! He also spent more than 13 years in Starfleet, serving with Humans! To be confused about Human emotions and culture after all that time, he would have to be very stupid.
Spock obviously knows more than enough about Human culture. He just pretends he doesn't, or he criticizes Humans for their "illogical" ways, because he is a half-Human who has loads of identity issues and is trying desperately to be the most Vulcan Vulcan ever.
It's hard for me to take Uhura's conversation with Spock too seriously. In the same episode, where you think she has a crush on him, the salt vampire reads her mind and reveals her fantasy man -- and it is not Spock. It's a handsome Swahili man. You are welcome to insert the idea that he would have to be Black to satisfy the racial attitudes that existed, but if they were alleging a serious flirtation between Spock and Uhura why wouldn't they be consistent and show Spock as her fantasy? The alleged "taboo" was already displayed according to your interpretation. Why be inconsistent?
People can't be attracted to completely different people? Happens all the time. How come Kirk fell in love with a strong activist like Edith Keeler (also, incidentally, a brunette white woman) as well as with a childlike blonde android Reyna, and submissive Native American tribal princess Miramanee? Why be inconsistent?
Spock didn't have to be her ultimate fantasy for her to be attracted to him.
Good you brought up the M-113 creature and 'fantasy man', that reminds me. How about this possible interpretation (which occurred to me when I watched the episode, not the first, but the second time):
Uhura is not joking when she says she is tired of hearing the word "frequency". (Funny that this scene was in the first aired episode. Those lines get a new meaning when you've seen all of TOS, and you know that saying "Hailing frequencies open" is the only thing she does in most episodes.) She is a very serious professional, dedicated to her work, but sometimes, like everyone, she feels a need for some romance in her life. (In fact, this may be seen as reflecting what happens to all of the crew in the episode: they've been in space for a long time, and many of them probably haven't had any sex or romance lately; and the M-113 creature is using their erotic fantasies to get to them.) Or if not that, then maybe just a bit of flirtation. Spock is someone that she finds attractive and intriguing (which doesn't mean that she is in love with him or anything that serious), maybe even more so because he is stoic and emotionally distant, but she's aware that he's unlikely to respond. She tries to flirt with him, maybe not really hoping for much but trying to get some sort of reaction from him. Of course she can only do that if she is teasing him - what else is she going to do, get all mopey and whiny like Chapel? Haven't you ever seen someone tease a person they find attractive, making a real attraction easier to show by pretending to be joking? Happened in school all the time.

(I also find it more likely than the idea of Uhura pretending to have an interest in Spock just in order to mock him - that would, to me, feel nastier and not so friendly.) She still gets annoyed with him for his typical unresponsiveness - it's probably not a coincidence that. just seconds later, she gets really angry at him over his lack of emotional reaction to a crewman's death (at least I presume that she doesn't normally berate him for his unemotional behavior on every occasion, as they've certainly known each other for a while and his personality is not new to her).
Later on she meets the M-113 creature. It reads her mind and presents an image of what she thinks her "ideal man" would look like (it's obviously not a real person; she thinks he's a crewman, but she hasn't seen him before). Some time before, she was frustrated by Spock's unresponsiveness. Spock is an alien, from a different culture, as different from her as anyone on the ship can be, since everyone else on the ship is Human (which can also make him interesting and exotic to some Human women, as Uhura's song in "Charlie X" suggested.) And now, how was she imagining the man she would have a relationship with? Human, of African origin just like her, even speaks Swahili... in other words, as similar to her as possible. And also very obviously interested in her. It actually makes perfect sense that, after having had another confirmation that a relationship with a Vulcan could never be possible, she would start thinking that what she needs is someone she has a lot more in common and who would be perfectly suitable for her in every way.