30 yr old speakers- time to replace drivers?

Degradation in SQ with rubber surrounds is brand and design dependent. I do not know your speaker.  In a vacation home in Vermont I have a vintage system used for background music, with 1981 DCM TimeWindows, with rubber surrounds.  It has been published that the drivers in this brand and model have longevity. There is no change in durometer of the rubber or SQ of the speakers from my experience. However, they sound like 1981 vintage speakers, through good ones for their day.  If needed, I would not invest any money in them even though they have sentimental value. There has been so much improvement in speaker design and SQ at all price points that I would go new. 

It’s nice to know the cut off for speaker value is 30 years ?? Pompous load of Doodoo, I think the First consideration should be the quality of the product. A Hi end excellent speaker of the past will still put many to shame today. I’ve people in my group with the likes of Tekton to B&W, Sonus Faber, and more, they’re happy I’m happy. My Infinity IRS system is spectacular and hands down considered the cream of the crop in that group. Granted you need the space having that, next was the total expense… middle of group !  Refurbished I’m good for years to come. It’s a hobby you can rebuild, modify, great sound doesn’t have to equate to great money. 

If they sound good and the surrounds are fine, use them!

I have a pair of Boston Acoustics A150’s. I’ve re-coned the woofers but sound excellent still. 40 years old! Point being yours can sound great, too. If the woofer surrounds are not disintegrated and they sound good I’d say leave them alone.  If you can eye-ball the caps would be good to make sure they're not leaking.

I have a pair of Bozak Urban 301 that are 60+ years old that I enjoy the heck out of.  After I inherited them from my father circa 1993, I have had both 12” woofers reconed, and refoamed; replaced one tweeter ( because I damaged it accidentally) bought on eBay; replaced the crossovers with OEM with the Pat Tobin mod, also bought on eBay; rewired internally; and, refinished the cabinetry. Total cost—not counting my own labor—I estimate to be less around $1000-$1200, spread out over a period of about 20 years because I didn’t do it all at once. For instance, I just had one of the woofers reconed and refoamed for about $75 plus shipping. And, these speakers sound fabulous. I have no way of comparing them to contemporary speakers, but as long as I’m happy with their sound, that doesn’t matter.

As an aside, I recently had my Thorens TD124, that I also inherited from my father, rebuilt to look and perform as if brand new, but for about 3 times the cost of the speaker refurb. I still have his Pilot amplifier to have rebuilt, but for now, I’m enjoying playing music on my vintage turntable, through my vintage speakers, attached to my “modern” Yamaha home theater amp. 

My point being: if one derives  pleasure from  “vintage” speakers, it doesn’t cost that much to have them refurbished when and if necessary to keep on enjoying them.