Do amps degrade over time?

Transistors also degrade over time but it usually takes longer than 15 years. By the time the unit is 30 years old one can expect a higher noise floor, not only from the transistors but also the resistors. Corrosion can also cause semiconductors to fail for no apparent reason. This is usually a problem associated more with ICs but it can certainly affect discrete devices also.

For now though, since you already have the power supply filter caps replaced, I would expect no worries for quite some time.

Second Thesoundhouse. Some of those older circuits are truly SOA. The right tech with the right upgrades will give anything current a serious run for it's money.

Thanks for the responses. My upgrade bug has been satisfied (and my wallet lightened) by recent purchases, so I think I'll be hanging on the amp for a while.

I have a 1975 Marantz 1060 bought recapped at least 15 years ago and it sounds terrific.  I even ordered a newly rebuilt 1060 to have as a spare for about $500.

These are full featured integrated units with three click stop tone knobs for bass,  mid and trebble.  They also have terminals for a second remote speaker set. 

Mine feeds Bluetooth 5.0 from an audioengine b1 into four KEF 104s also from 1975.  I judged these the best sounding speakers being sold in the DC area at the time. Sound quality of TIDAL master streaming approaches my high end SACD player and even some vinyl. 

The 1060 was one of the first sold state amps Marantz designed and some people claim it somewhat mimics their previous tube amps, though I don't know how.  I recently bought a tube amp but have not yet fired it up.