I think that capacitors are the first things to go. Somewhere in the 10-20 year range depending on the particular cap. They can be easily replaced though. Other than that, deterioration will probably be caused by environmental conditions rather than due to usage over time. The time it takes for environmental deterioration such as oxidation to take place will depend on the conditions in which it is kept. Many audiophiles change their equipment so often, they probably don't have it long enough for significant deterioration.
When I think about how many audiophiles have their system down in their basement, I wonder if they've ever popped the lid on a component and looked inside after a couple of years. I have some filing cabinets in the basement. Even with dehumidifiers going, I'll pull something out of the cabinet and the staples have turned to rust after a year or two. It's frightening to think what's happpening to the innards of components.
When I think about how many audiophiles have their system down in their basement, I wonder if they've ever popped the lid on a component and looked inside after a couple of years. I have some filing cabinets in the basement. Even with dehumidifiers going, I'll pull something out of the cabinet and the staples have turned to rust after a year or two. It's frightening to think what's happpening to the innards of components.