I have been buying and selling used audio equipment for over 45 years and will assure you that that any pair of speakers that was built by a well known and respected manufacturer that originally sold for $40,000.00 will not sell for $4,000.00 ten years later, unless they are stolen or heavy damaged, the average price of such speakers would be $13,000.00 depending on condition. After consulting several experienced techs who have worked on $40,000.00 (there is not many) all agreed that the quality of the crossovers and drivers in a $40,000.00 speaker that is ten years old would be considerably better than a new speaker that cost $4,000.00 or even $13,000.00 today.
We don't normally invest in speakers that are over 15 years old (unless there classics) and most of the problems we encounter with speakers of that age is not from parts going bad but rather from misuse and or abuse, a few examples are (1) Exposing a speaker to direct sunlight for ten years will fade the finish and deteriorate the surrounds (2) Over driving your speakers or clipping your amp, can get you a big repair bill or maybe worse, the knowledge that the speakers can't be repaired at all.
We don't normally invest in speakers that are over 15 years old (unless there classics) and most of the problems we encounter with speakers of that age is not from parts going bad but rather from misuse and or abuse, a few examples are (1) Exposing a speaker to direct sunlight for ten years will fade the finish and deteriorate the surrounds (2) Over driving your speakers or clipping your amp, can get you a big repair bill or maybe worse, the knowledge that the speakers can't be repaired at all.