Except of electrolytic capacitors electronic components nearly don't age - and the basic components are cheap, very cheap indeed. (Enclosures, transformers, vol pots are the main cost factors.)
Design faults set aside, the quality of the solder joints plays a role, and leaded solder joints are supposed to live longer and crack less often than leadfree ones - and in my impression, the longevity of through hole components is better than the longevity of smd ones (not to mention repairability.) Take a look e.g. at northridgefix electronics repair (nice program for relaxation): failing capacitors (not electrolytics) en masse, through-hole capacitors (from wima, e.g.) nearly never fail.