Don't count out how much pull Kirk (an Admiral) had in the decision. He could have pushed to refit over replace.
That's a good point. And not just any Admiral, but Chief of Starfleet Operations.
I'm just glad they did the upgrade. The nacelles on the TV version of the Enterprise always looked super weak to me and the refit nacelles were a nice step up. I also loved the torpedo bay. The refit Enterprise is still my favorite ship design.