Thoughts on extending speaker life.

Age can deteriorate any part, cone, surround, you could burn a voice coil, ....

I have speakers with drivers made in 1956. The tweeter horns and mid-range horns appear to be bulletproof, 63 years old, still sound terrific. I do have spare drivers waiting (as someone else said, they were made in 1956 also, they just haven't done any work).

The 15" woofers (paper with flexible pleated cloth surrounds), this one

https://reverb.com/item/2307415-electro-voice-model-15w-alnico-magnet-15-woofer-new-in-original-box-nos

I had them re-coned professionally many years ago, have a spare waiting, and re-coned one myself not long ago.

Videos show how to do it, cost is minimal, the hardest part is scraping the old glue off the spider ring.

http://www.speakerworks.com/speaker-repair-kits-s/65.htm?gclid=Cj0KCQjw3uboBRDCARIsAO2XcYCQUY1lUVYTubmOssOLwtflmQlsxhhxHHnNrms9nKalZrIaNGzk2ngaAqehEALw_wcB

Based on the success, I re-coned my Velodyne 12" sub, it went well also.

I used to think about 'sag', especially such advanced years, but there is no evidence in mine. The voice coil would rub, you would hear it for sure.

I should have said, 

15" I replaced the coil, cone, surround

12" I just replaced the surround, the cone and coil were fine, and getting the voice coil centered was easy after watching the video.

I am and will continue to use my 1975 Larger Advent speakers connected to a mid seventies  Crown DC300A power amp and a Kenwood C1 Preamp as my living room - main speakers. I have had them re-coned (new foam replacements and old remaining components) three times. Haven't checked, but will most likely have to have them re-coned again. Absolutely worth it.

To keep my 80 -50 year old speakers working well I play them and keep them dry and out of the sun 

@johnk --

To keep my 80 -50 year old speakers working well I play them and keep them dry and out of the sun

Wouldn't you say regular (certainly weekly) use of one's speakers, apart from other named factors, is a vital part in keeping them "up to speed" over time? It seems to me an overlooked aspect in the discussion of how to favorably maintain the performance of speakers through many years.