Are advances in technology making speakers better?

They'd need to prove to you first that what they are offering to upgrade to is significantly better for you.

With the ongoing materials and components shortages, this may be not the case.

For instance, I remember a decade ago neodymium magnets were used in many new speakers, even budget ones. Now they are rarer. Ferrite rules.

I'm still running with Epi 100 speakers in two of my systems (Minnesota cabin and bedroom suite) from 1979... still excellent, w new caps and binding posts, and of course woofer foam or new woofer from Human Speakers.  Not trendy, and neutral rich pleasing enjoyable speakers; no need to get new.  They, or should I say Winslow Burhoe the designer, had found a "sweet spot" design, that model, and then later iterations degraded it.  And, as the other posters have pointed out: a lot of times newer models are simply for marketing, because the companies are expected to bring out new stuff to sell... doesn't necessarily mean it's better stuff.

Likewise the very first Bose 301 bookshelf was, and is, a pretty darn good, enjoyable speaker for almost everybody except perhaps discerning audiophiles, but even I still like it for general casual listening... but the LATER versions of the 301, the II, III, and IV, were not as good... so newer again certainly does not necessarily mean better.

That said, the new Klipsch Heritage line, the mk IV, are supposedly better than the previous I, II, and III... so, progress can be made.  Likewise the newer JBL 100 and the KLH model 5 are supposedly better, according to various critics, than the older versions... but note (as @skyscraper points out) that the new models were a LONG time coming because the old models were already excellent.

And, all that said, I think one thing that HAS occurred is that we are now in a new golden age when it comes to the LESS EXPENSIVE speakers out there, the lowers in the lines, so to speak(er), as they have inherited trickle down tech.  Examples are the low-cost Andrew Jones-designed Pioneers,,, or perhaps the Q-Acoustics Concept 50 at $3000 which borrows from the Concept 500 and apparently from what I've read might actually be even an improvement over the Concept 500 at $7000...  $3000 isn't really inexpensive, but it illustrates a point.  Another example is the Polk R700, which has garnered stellar reviews vs. higher cost speakers including the higher cost Polks and again has inherited "high end tech" genes. 

But speakers under $1000 these days if you choose carefully can be stunningly good for most home applications.  

and, I do agree with what most of the posters here are saying: why switch out if you like what you have?  

my 1994 Lexus 300 is comfortable and reliable and still runs beautifully.. sure a plug-in hybrid would be nice, but at what price?  I'm rolling w my old Lexus as long as possible.

Yes.  By definition, Advances in technology always makes technical products better.  

If you are confused and thinking you should probably upgrade without really knowing why, then the marketing compaies are earning their money.

Jerry

"Advances in technology always makes technical products better"

well.......

advances mean an improvement in one or many aspects. Which then have to be applied to the product in a way that it improves the product. Not trivial at all. 

The famous story is with the Ferrari F40: when the F50 came out, with better measurements in every aspect than the F40, it was still slower. Engineers spent months trying to figure out why. At the end they just conceded, sometimes awesome design is just hard to beat, it's not only about improvements.