I have friends who also think "Amazing Grace" was a terrible thing to play at a Vulcan;s funeral.
I disagree and think it was a great choice. Wasn't part of TWOK about Spock accepting himself, his human half. TWOK is littered with examples of Spock's (In can't think of a better way of saying this - I mean something between love and affection so I'm going to say) fondness for Kirk, McCoy, Saavik, the Enterprise, his crew.
Spock once was lost but now was found, was blind but now he sees. Spock accepted himself in TWOK, his friendships, his duties and responsibilities as a Starfleet Captain just like the hymn literally says.
Shatner was so great in the funeral scene. One of the greatest movie scenes in Star Trek IMO.
I don't care that it wasn't Vulcan enough. Spock didn't owe Vulcan anything. Funerals are not really for the dead. They are for the survivors. This is the way his friends (and real family) showed their respect to Spock