it’s a function of materials used and when they deteriorate. Foam surrounds have a 20 year(?) life. Anyone that recones drivers should be able to answer.
My experiemce….I heva 20 year old thiel 2.4’s that as afar as I can tell sound as good as the did 20 years ago. They were 4500 at the time, which I would call resonanbly high end. Generally their reviews are mostly positive.
Upgrade? I see no reason to, An upgrade would likely be expensive, thus costing me 16k or more. Seems silly and I’d probably be lucky to get away for 16K for the pair,