Capacitors have improved in certain ways due to designers looking and wanting a different type of sound than previous versions. The change in sound is due to using different materials and construction. I can say that the early capacitors due not sound bad at all if given time to re form in an old component. You have to give some time before you judge an old capacitor especially in an amplifier or speaker because most of the time they are not bad at all they just need time to play and re form. If you do change the capacitor to a new one it can sometimes cause the gear or speaker in question to sound very different, especially bright at first, due to the new cap needing to form as well.
