From what I gather, not having read her book, getting on screen in TMP after her low point in life must have been a huge boost for her, and I think she was recruited for the film largely as an act of kindness.
I thought it was great to see her in TMP, although her part was so small that there wasn't much she could do with it. Still, it felt like her best acting days were behind her... and she never did much else after that (it doesn't look like she ever started a family). She has participated in the Star Trek Phase Two fan episode productions and her acting ability there came through a bit rough around the edges, feeling a lot less refined than her early TOS work (to me anyway).
Back to the original topic... Even when I first saw this episode as a kid, I couldn't help but notice that the kiss between Kirk and Uhura wasn't really "complete". It's obvious how you see Shatner's open mouth exposed, not making a complete seal. This was in stark contrast to Nimoy and Barrett, who clearly had full lips contact. At the time, I just took it as Kirk's resistance to follow through, knowing that a full kiss may weaken his resolve to resist. Who knew how far it would go? The Platonians might've ended up having them copulating on the floor for their amusement.
Anyway, it always seemed to me that "first interracial kiss" was over-hyped for what it truly was in this episode.