" If you write a script, you're certain that the changes made will be identical on each box. If you're doing them all by hand, you aren't.'"
No... if you write a script, you're certain that the change ATTEMPT made is the same. The changes may very well not be the same, if one of the boxes is messed up, but you can be certain it wasn't because you did it differently on that box. That's the difference between a GUI and a CLI... you get a same attempt guarantee, which allows you to blame the box instead of yourself when management comes asking why it failed.