I moved this to the Farrell thread, so as not to hijack the other thread.
I disagree with your thinking in your first paragraph. Just because a run did not score or a play did not lead to runs, that does not mean that a play was not as significant to the outcome of the game as a run scoring play was. Price's pitching in the 7th inning last night to keep the Astros from scoring was a pretty big moment.
Now, I absolutely agree that some plays have more leverage than others. That's obvious. That means that some managerial decisions have more impact than others. That said, because there is no way of knowing what might have happened in the alternate scenario, you have to go by run or win expectancy before the play happens. And the difference between leaving pitcher A in the game versus bringing in pitcher B just isn't as large as people think. There's a difference, and there is a 'right' call statistically. But that right call might be so insignificant that Farrell's judgment based on intangibles might trump the statistics.
In the above mentioned case, the difference between leaving Price in to face the batter versus bring Reed in was probably very, very small. However, if Price had given up a grand slam, the decision not to bring in Reed looks huge, after the fact.