The big difference is in manufacturing tolerances. Back in my early days in electronics (60s) 5% or even 10% tolerances in values were frequently used because it cost money to get to 1% tolerance or better. MilSpec parts often had to measure far more accurately than consumer electronics. The same was true for inductors and resistors. The simple truth is that a 50 microfarad capacitor that accurately measure as 50 mfd will sound the same as any other that accurately measures as 50mfd. Depending on the values of the other components in the circuit you cannot hear the difference, assuming they are all accurate to a given tolerance. Usually, the differences in rated voltage and tolerance are used for the purposes of obtaining longevity and reducing failures due to arcing which results in a short circuit.
The other truth is that snake oil salesmen are far better psychologists than most university PHDs. They have been around a long time because they know their craft and it works.
The other truth is that snake oil salesmen are far better psychologists than most university PHDs. They have been around a long time because they know their craft and it works.