It depends where you are referring to . IHave been into Loudspeaker mods for years ,and without question are upgrades in Sonic performance ,with Capacitors Resistors sometimes inductors, wiring, connectors. For the vast majority of Loudspeakers use cheaper parts quality ,why cost.
this is true also in electronics , types ,electrolytic in power supplies ,which should v be bypassed with a decent quality .1uf poly cap it smooths the upper frequency noise ,and quality here too very important like using a Elma Silmic cap much smoother ,or top Nichicon caps , even Clarity,or Mundorf 4 pole caps .
for coupling caps where a good poly cap, or top Copperfoil like World class Duelund ,which BTW I have been using for years I just exchanged the very hood Jupiter copper foil for the much better and muchBigger DuelundTinned Copper foil paper oil in my preamps output section , they take many hours to settle in but well worththe efforts.