Great points all around.
I am of the opinion that good writing and a good story is where the characters make their own choices, so to speak, and not the writer really making the choice for them; i.e., organic, without bias. "We have to kill Kirk at the end" is not good writing; he just dies at the end of a good story because that's how it flowed. Someone is going to ask, "What about how Spock died at the end of Wrath of Khan? They wanted that to happen!" No, they didn't. They wanted it to happen near the start. It got pushed back as the story was developed.
Not to rain on your parade, by Spock's death scene was changed due to plot details being leaked-some rumors even suggested that GR was behind the leak due to his dissatisfaction with TWOK and its story. I have not been able to verify that.
I find STID to be quite organic, especially in Kirk's death. Given Spock's willingness to die in the volcano at the beginning it would not have surprised me if he had ended up near death. But, Kirk sacrificing himself felt like it flowed better. Kirk had a choice to make and he chose to sacrifice himself.