Buying used vs new speakers from a technology perspective

Of course, there are new speaker models every year that have new materials, new crossovers, and new cabinetry. Rel has its newest S/ series or B&W has a new diamond series. We often equate "new" with "improved." In the audiophile world, however, "new" is probably just "different." You might like the difference; you might not. Manufacturers will describe how the latest model is an improvement over the last one--the sub has a stronger amp, a stronger cabinet, a new material for the speaker cone that doesn't lose its shape. And as much as I am interested in the latest and greatest, I try to remember that it's the sound that matters, not the version number. 

i use proac tablette 2 that has been upcycled over the years. the last refresh was putting in pathaudio resistors

Depends on how far back you go.  Example: speaker surrounds before the early-mid nineties were made from perishable materials.  Not anymore.  However, electronics always age but in my experience fail only occasionally.  A ten year old speaker should be fine unless it was really abused - which is rare

How can someone upgrade an old speaker with new technology and then say see how good my old speaker sounds? 

My AR 9's from 1979 still sound GREAT what a find used