That's like saying I like the nostalgic blue smoke from the worn out rings in my original 66 Mustang. Different strokes I guess.
Well actually, if it had the blue smoke symptom it would be sonic disfavor, then a replacement would be indicated. I agree that the sound that each listener prefers is very subjective.
Part of the appeal of old amps, for me, is the subtle degree of fatigue that occurs with parts before they fall "too far" out of spec. In other words "broken in". Not everyone likes their blue jeans stiff as when they are brand new, some like them more broken in after multiple washings and wearings. Eventually, when the jeans do wear out, then replacement is indicated.
So I guess I am saying that there is an acceptable degree of normal wear on old electronic parts, and that degree of wear might be sonically desireable to some individuals. IMO, the wear contributes to the "vintage sound". And those degrees may vary according to an individual's sonic taste. That is my only point.