From my reading it is the electrolytic caps which deteriorate with time and change value. If your crossover contains any of those they will be the candidates for replacement.
"Upgrading" any other caps will more likely be a matter of taste. As rcprince suggested, it may not necessarily be better than what the speaker designer chose.
"Upgrading" any other caps will more likely be a matter of taste. As rcprince suggested, it may not necessarily be better than what the speaker designer chose.