People often have their amps recapped unnecessarily. Many amps can go 40+ years before a capacitor goes bad.
More often, in class A and A/B amps, the bias drifts.
Outside of Class D and THX AAA designs, amp technology really hasn’t improved much in the last 35 years. Buying a flagship amp that is 20 years old but in great condition is a good way to get top-shelf performance for reasonable money, even if you do have to spend $1K to have it refurbished.