ahhh, just to put my oar in.
While I don't believe all the high end audio snake oil claims about
this or that brand of capacitor. Going through a good quality amp and
replacing the coupling/filter caps with polypropylene polystyrene types
can make a subtle but audible difference even to the non "golden eared"
set.
Yes it's a lot of work and finding all the right values can be
difficult and expensive. And the plastic film types tend to be 2-3 times
larger, which can be a problem.
Is it worth it? good question. If it ain't broke... If your amp is 20+
years old just doing a general replacement with new capacitors, fancy
one's or not, will probably make a world of difference. Also if the rest
of your system is not "up to snuff", the difference might not be
noticeable.
As a first experiment try replacing the capacitors in your speaker
crossover. There size is usually not a problem and you can gang 'em up
if needed to get the right value. If that makes a discernible difference
to you then consider pressing on.

good luck and have fun, tomh