Hi Roxy. I have a 30yo Denon PMA-520 that used to sound great. I am the original owner, bought it from the original Magnolia HiFi in Seattle back in 1995. It has sat in climate-controlled storage for the last 18 years or so, unused. I fired it up a couple of months ago, let it sit for a few days before running a signal through it, then played it and it sounded quite wooly. I suspect I need to have it re-capped before I pass it on to my daughter.
I don't know if it makes a difference if a device has been used regularly over many years or if it has sat unused for many years. My gut tells me that sitting unused has more of a detrimental effect on capacitors. Others more knowledgeable than me might be able to shed some light on that question.