Lifespan of amps and preamps?

Hello.  I have been listening to the same NAD 1240, Adcom GFA 535, and B&W dm 620s since I was 20 in 1990 (it was a big deal to buy all that as a 20 year old kid...).  Other than doing a thorough cleaning on the adcom a few years back when it stopped working, I have literally done nothing to these components. 

Are they totally dated, meaning past their intended lifespan from an internal component perspective?  I have to say it all still sounds really good to me.  But I never really listen to other systems.
Thank you for any input!
Scott.