I think that keeping them in a controlled environment away from heat, moisture and sun would be your best bet! I have a pair of Acoustic Research AR9 speakers from 1980 that are in excellent shape and can handle anything I throw at them. They were very well cared for.
???Modern Speakers???Life Expectancy???
The demise of my 20 year old amplifier has me thinking about this a lot lately..I have speakers that had manufacture periods starting in late 2012(Harbeth M30.1)& 2014(Dynaudio Excite X14)..Both are low hours usage & it's likely neither is over 300-400 hours use..At 63 years old & failing health is it likely I will outlive the speakers or that I will need replacements in say the next 10 years?Is there any preventative maintenance that will keep them fit for duty?Thanks much all.