I think the romance worked very well, in addition to being a complete surprise. It was low-key, as you'd expect given that Spock's got even bigger issues on his mind then. It showed Uhura being driven by compassion and sympathy, which was nice, and tied in well with her occasional flirting with Spock in the original series. It was also set up, albeit subtly, during earlier scenes in the film - Uhura's assignment to the Farragut, for instance. Spock avoiding the appearance of favouritism, or sub-consciously avoiding some feelings he'd rather deny?
I like the new version of Uhura a lot, too. More forthright and assertive, but retaining her typical passiveness when the situation calls for it. Kind of like a mix of the best elements of 'young Uhura' from the TV show, and 'mature Uhura' from the movies. She was a ludicrously under-developed character originally, so it's nice to have her getting some serious respect and significance.
Besides, Spock has been - and always shall be - hot as hell. Women have been dribbling over him for four decades now. Who's to blame Uhura for going down that same path?