Dover, How do you discharge PS caps? Turning off for day or 2 may not do the trick and still keep'em charged. It's highly recommended regardless of unit being turned on or off to discharge caps with 1mOhm resistor before any 'surgery' on electronic equipment for certain reason and if you want to verify it, you can (certainly with your own health risk) touch terminals of your power supply caps just to verify and test the information you currently believe into.
As to sound differences, you're simply listening to the 'colder' rig than one was running for a month 24/7. Speaking of electronic components, normal operating temperature is very important to have specified parameters, but excess of temperature can also be even more destructive. In solid state electronics the vibrations against heat sinks will cause loss of integrity and certainly higher running temperatures. In tube electronics in general LOTS of components exposed to the hot running temperatures. It also tells that turning off even solid state devices, will prolong length of good performance.
If you keep recharging a battery before it is discharged fully, it can form a "memory" whereupon it wont work any more when it reaches that point that you kept recharging it, whereas if you completely run the battery down before recharging, then it will work at all levels.
Can you specify what kind of battery has such phenomenal capabilities?