I recall hearing that the Mormons gain very few converts from their missionary program. One of its biggest benefits, however, is the personal growth gained by for the young people who participate.
That's not surprising. The journey often produces more insight than the destination. As Dwight Eisenhower noted, "Plans aren't important. Planning is." We see the wisdom of that every time we watch weather pictures produced by space satellites or use the collection of other products that came in the wake of putting man on the moon.
Although we realize the importance of incidental benefits, when a decision is evaluated the traditional approach is to assess whether of not the goal was achieved. To do otherwise is mocked as the equivalent of "The operation was a success but the patient died." That line sounds clever, but its wisdom evaporates upon reflection. We frequently learn more from failure than from success and the person who has been punched in the stomach a few times probably has a keener view of reality than those who've glided from success to success. Thomas Edison denied that any of his experiments were failures. He viewed them as revelations of what wouldn't work.
Should we evaluate whether the efforts achieved the goal? Sure. But while we are doing so, why not also consider what was learned and strengthened in the process? Ultimately, those incidental benefits may produce far greater results.