So I am trying to understand this topic better...

I am a guitar player and I always prefer the sound of older "broken in"
speakers over new identical ones. They have all these new re-issue
speakers
but I still prefer to buy used ones on ebay. The new ones sound less
resonant to my ears, especially when pushed to gig levels.

Is this difference an actual acoustic difference or psycho acoustics? is
my
mind playing tricks on my ears????

Fellow guitar player here.

It's a mixture of both. We know that different guitar amps and spkrs have
distinct sounds. Hell, many of us can pick out the sound of certain
amplifiers/speakers by simple listening (assuming it hasn't been immersed in
effects). There are indeed acoustical differences, mostly categorized by
the outrageously high distortion content of most guitar amplifiers and their
spectral distribution. But there are indeed some psychological aspects at
play as well.

In other words, there are real differences as well as "fake" differences in
those cases.