Just relating my experience. I purchased a pair of Polk SDA-SRS speakers from the 1980's just a few years ago (4 tweaters, 4 mid and 4 SDA drivers and a large passive radiator). I have always enjoyed the tremendous sound stage of this technology since I first heard a pair in a hi-fi shop shortly after they were released. There is a large SDA following on the Polk forum. One of the outcomes of this group is that some of the technically talented have put together several items to 'upgrade' these rather old speakers. The most significant upgrade is to recap the cross-over, and there are schematics for each of about a dozen SDA speaker models that were built during this time. When I got them setup I thought they sounded great for a relatively old set of speakers. Good sonic attributes, but a soundstage with more width, depth and vertical than I have ever heard. But I decided to rebuild the crossovers using the high-end caps as suggested by the forum members. When I finished and fired them up for the first time, it was like someone took a very thick audio absorbing blanket off from over the speakers. In spite of what I appreciated as great sounding speakers, and I auditioned some $10-$15k speakers prior to purchasing these, it is hard to describe the improvement of every sonic aspect with the new and upgraded caps. My point is not the SDA speakers, but the sonic improvement due to the upgraded caps. I have not done anything similar with electronics, i.e. amps. But if it is anything like I experienced with speakers, it is well worth the investment.
re capping
I hear the phrase 'recapping'. when do you know when you should 're cap' an amplifier? I have a McIntosh mc602 amp that sounds fine to me. I also have a McIntosh mx132 that works ok for me. I also have a bose 901 series 2 active equalizer that seems to work ok. the 'red' on light kinda flashes now and then. if my system sounds ok, should I worry about my units?