When you think about it, the basic construction and electronics associated with speakers has not changed that much in 30 years. The biggest detriment to older speakers was the use of "foam surrounds" to connect the speaker cone to the speaker frame. They turn to dust over time. Speakers with good rubber type surrounds can, and do, still sound great. A great 30 or 40 year old speaker can still be a great speaker today - not all are, but many have survived the rigors of time very well.