re capping

It depends what do you mean by "much better".  Do you mean lower inductance, like slit foil caps, that are very expensive, or lower ESR caps that might cause rectifier damage?  When you recap 30 years later original capacitors don't exist anymore, but I would check their specifications and look for something similar and not the "best" available.

True, dat.

EG, a electrolytic with a much higher frequency response, or lower impedance into higher frequencies...might make an amplifier oscillate out of control, due to the feedback and loop gain being set too close to the limit and part of said limits unintentionally relying on the original capacitor’s limits. It can be done. It happens more often than one thinks.

Willy nilly cap replacement by people without the understanding of the circuit, can result in circuit failure. Or over-stressing that can kill the circuit far sooner than the original design and build intended.

Let’s try a hopefully humorous analogy.

Most solid state audio circuits turn on, when that power switch is hit...like they were punched in the head with a ludicrously high speed truck. Hit the power switch and everything in the box goes *BANG!* (Ok, we’re all awake now, pedaling our little bikes!) Somehow they survive it. Robust little things, generally speaking.

If you get in there and make capacitor value and capacitor quality changes, it’s like adding in bigger and faster truck change-outs... to the circuits which were originally being punched in the head by big and fast trucks. This is generally not a good idea.

Somehow this didn't get said, so I'll describe the modes of failure. 

Caps fail in a variety of ways. Their capacitance diminishes or rises. Their equivalent series resistance rises, and they leak DC, otherwise called "leaky" or "electrically leaky". Often a failing cap will exhibit some combination of these symptoms. It's not at all uncommon for a cap to measure higher capacitance, but that usually means it's leaking. Leaking interstage coupling caps will slowly destroy your amp so just because you're not hearing some obvious sign of trouble does not mean there isn't a problem. High ESR is just like putting little resistors in series with the cap and the problems with that are hopefully obvious.

Heat destroys electrolytic caps. That's just a fact. The more heat applied and the longer it's applied has a direct relationship with the life of electrolytic caps. Anyone who says otherwise is a liar. 

@kosst_amojan You seem very sure of your facts. YOUR facts, YOUR truth. What about others’ facts and truths?? 🤔

The Truth is available from the manufacturer.
Sometimes the Truth is optimistic and sometimes not.
Life is predicted based on science and math, but can vary widely due to variation in sub contractor supplied materials.

We once replaced 7 million 85°C/35V electrolytic caps with 105°C/50V version from another manufacturer. All was well for a while until we found that the replacement would fail if the bung was over the -18v rail. The potential sucked out the electrolyte and started fires once the electrolyte reached the positive rail.