Amp showing its age?

In your loudspeakers most likely the coupling capacitors ,I have been upgrading Xovers for years ,stock Xovers are in most cases average at best to save $$

upgrade-these capacitors and your speakers will sound better then before 

as long as the drivers are still in good shape.

The speaker caps are probably OK if the new amp is working fine with them.Speaker crossover caps will go bad, but not as quickly as amplifier caps, 30-40 years. If you were using  vintage speakers made from 1950s to 1970s, then replacing the crossover caps would make sense.

Years ago I read an article whose author stated  that as a rule of thumb,  capacitors on solid state power amplifiers should be replaced every decade or so.  This is even more pertinent when the amplifiers receive a lot of use. 👍

@lynn_olson  Mine is a case of gradual relaxation on driver grip, most noticeable in the bass. I was actually enjoying the bottom end end harmonic distortion, but when a notorious high amplitude signal in the low impedance frequency range threatened to blow the left speaker, I knew the time had come. Being impatient, and having no repair shops anywhere near, and also curious about the new iteration of Coda S5.5, I simply switched it in for the Parasound, quickly heard the difference, then posted this question.
@ audioman58, @chenry I'm not worried about the speakers, given that a new amp quickly removed their flabbiness. They are a little newer than the amp and now sound fully restored. So I now feel confident that their useful life without repair will exceed my own.

Depending on the model of amp it could be worth it to get it repaired. For example, I have a Krell KSA 300S from the mid 90's that I bought new. It worked fine for over 20 years and then died with a puff of smoke. I was lucky that there was a qualified repair technician (Gig Harbor Audio near Tacoma Washington) that was within a couple hundred miles. They were able to send a key module (output transistors I think) to Krell in Connecticut for repair and replace the capacitors themselves. This avoided shipping the whole unit from Washington to Connecticut which would have been nearly $2000 (this amp weighs 185 lbs without packaging).

The total cost of the repair was about $3000 and the amp is worth $4k to 5k on the usesd market so it was an easy decision. It's driving a very difficult load (Thiel CS6) and to replace this amp with a new one of similar capability would have been tens of thousands of dollars.

Hopefully anyone who buys a 20+ year old SS amp knows that the capacitors will need to be replaced. If you sell the amp make sure that you state it is in original condition. The amp is likely to fail soon and if it was me I would clearly state that the amp needs service and the buyer needs to take that into account.

The last thing I'll mention is that it is hard to get rid of a monster vintage amp because if it weighs over 150 lbs with packaging you have to ship it LTL which is very expensive. Also, if you don't have the original packaging you have to build a crate that accomodates a fork lift which is surprisingly costly, especially if you have it done professionally. If you don't go to extreme measures to package the amp for shipping you can pretty much guarantee that it will arive damaged. Most people selling equipment like this require the buyer to pick it up so if you are in the sticks you'll need to take that into account.