IMO, unless they are leaking, there's a lack of bass or a 60Hz hum that will not go away after a total recap of the power supply, which then points to the filter caps, I don't replace them. I do bypass them though, basically what that means is a 2.2uF 250v stacked film cap, 667-ECQ-E2225KF, is soldered across the terminals of the filter cap, and it takes over the filtering of the high end of the audio spectrum and makes a noticeable difference in that end.