When to get your amp up graded caps ???

I'm with Has2be, Wolf-Garcia and Liz.
Macs would less-likely need 'upgrade' or change for the better components which will probably be the waste of time and money.
If the time has come, you'll need to replace them with identical equivalents. To test caps(mainly DC) you'll need cap tester or DMM capable to measure capacitance in order to randomly pick up one of the crucial caps that you would like to compare to the rated values. Normally there's a lot of headroom for needed capacitance so if the DC caps loose their capacitance there's still a room to play more music before the replacement occurs. Hence you might be still OK to enjoy your amp.

I think it is sometimes necessary to "downgrade" the amp when one feels unworthy of the high quality of the sound.

The ten-ten-ten rule applies here. If your amp is over ten years old, it's time to think about a recap. If it's another ten years old it's time to recap, no thinking about it. If it's yet another ten years old, think Russian Roulette, 3 chambers live in a six shooter.

Peter B.

Russian Roulette requires 1 live chamber, otherwise it's just too dangerous.