To echo the good advice already given by Chris and jgarcia, I would say "If it ain't broke, don't fix it." Your insticts about doubting subjective statements are correct here.
Replacing internal wires or crossover capacitors, just for the sake of "upgrading" won't change anything. If the values of the capacitors (and all the other crossover components) are correct to begin with, then replacing them with more expensive capacitors (or other components) of the same values won't make an audible difference. There are some who claim otherwise, but no evidence exists to back those claims... and there are some very good DIY designers who have tried hard to find such evidence.
If you want to correct some flaw in your speakers sound, you must first be able to measure their frequency response to identify the flaw. If you identify an objectionable peak or valley, or a tonal imbalance, then you can design a different crossover to correct it.