The only two things I can convince myself to add to the discussion are:
It seems to me important for serious brewers to learn how to use all the standard techniques that have been used to make good beer. I've thrown decoctions into recipes when the temperature drops fast outside and I can't get enough hot water into the mash to hit my marks. Step mashing gives you an appreciation of all the different enzymes at play in various temperature ranges. Then when you're designing your flavors or run into problems, you have a few ways to get to a satisfactory result.
Second, I use a triple decoction for my Lenten brew of a BPA. It's not called for, but I use the excuse that it's how we can brew without technology. It feels more authentic for the participants, I have lots of hands that need something to do and it helps keep requests to teach brewing to people quite low. Beer that you had to suffer for seems to taste better and it eliminates the casual potential beer maker from drawing me into their new halfhearted hobby. We also do a 4 week bottle conditioning process to make it seem like it takes the whole length of Lent.
So there are practical reasons to have those armaments in your arsenal other than science or tradition.