How long should high quality speakers last?

I have several speakers that I liked over the years which I have kept and still using regularly. For example, B&W 801 Matrix S3, German Physiks Unicorn II and Borderland iV, Wilson Audio WP7, all over or 20 years old. I have a 3-way KEF that I bought as a student 40 years ago and still plays as new. All in original condition. Therefore they can last, if you take care of them and are held at appropriate conditions. Personally, I avoid upgrades, unless not functioning, which has not happened yet.

I bought a pair of JBL L-65's new in 1979. Refoamed in 1989. Refoamed again, crossovers rebuilt, and grille fabric replaced in 2023. They sound better than new now.

Eventually the materials with degrade. Usually this happens so slowly you do not notice any sound difference. It all depends on cone composition on all components.

I think you should enjoy the speakers and if you are not happy at some point with the performance and sound you can get them reconed. After that, they will need to be broken in to sound good.

I  have a pair of Canton Karat 200s (made in West Germany) in my vintage system that I purchased in the summer of '85. They still sound beautiful---the spring clips in one speaker is a little loose. Other than that---no problems.

Until you get the itch to upgrade?