Well... generally speaking, there are no modifications that have to be made on any amp. All amp modifications should be evaluated based on the sound you are after. Don't make changes just for the sake of a change...
But with that said, eliminating the master volume wire on these second generation amps will improve the sound no matter what sound you are after!!
The stock electrolytic capacitors are as reliable as any electrolytic... and all of them will eventually increase their internal resistance over time. It is usually much simpler to just replace them if you do not know their history. I'm not sure bad caps would cause a problem with volume... more likely increased hum and sometimes a self-oscillation called motor-boating.
An amp unplugged for 24 hours should be pretty safe to work on. I wait about a 1/2 hour on mine. If you are asking this question, then I would advise you not to go poking around with the amp plugged in under any circumstances!!