First of all, thanks for all the effort to research and model this!
A friend of mine did some modeling as well, and came to the conclusion that there should be a treble increase, rather than the perceived decrease:
Even though the exact values differ from your (probably more correct) model, the effect is clear.
So, what could we really conclude from all this? That our models are too simplistic? It seems like they contradict your empirical tests? One indication of the complexity is the fact that in your real recording example, the 12th and 13th component is really louder in the rolled-off case, right?
Congrats! That's a nice guitar. In the future, just go out and play them. If you want to know the difference between two of these track them down at a guitar shop and play them. Nothing is better than your own hear.
Thanks for the info! My little brother is learning acoustic guitar. Until now, he has learned different techniques like strummer, flatpicking or travis picking. His music lesson is going well under the trained professional and hope so he learns well and play beautifully!