pmbuko,
Analogies are good for explaining ideas, not making arguments. Just because leather and rubber loosen, doesn't mean metal, carbon fiber or whatever other materials you use in a speaker are going to change in a specific way to dull the amplitude of their high level notes.
A good example of why your argument isn't one would be to counter with the example of a car engine which supposedly gets TIGHTER and more aggressive with "break-in". But of course, using that would serve no purpose as neither are a speaker and neither employ the same physics.
