Maybe that's how your cables actually sound, after the tarnish & oxidation & crap is removed. Perfecting system synergy & component matching is certainly a bear. So you DON'T want to have everything voiced around filthy connections with compromised conductivity.
I had an old favorite dealer who would harp on the point that all connections in an audio system should be thoroughly cleaned at least once every year. You don't want to wait so long that you get a big sonic jolt after a cleaning.
Incidentally, I've heard that silver connectors don't need to worry about oxidation because "silver oxide is conductive" (e.g. Audioquest often touted this fact). But surely it can't be as conductive as clean pure silver, and is that black stuff really silver oxide or silver tarnish (or both) - I don't believe tarnish has agreeable conductive properties.