It strikes me that having the letter x twice in a name where it only belongs once betrays a lack of class. People who add the second x by choice are telegraphing their urgent need to get your attention. If they can't get your attention because of their talent, why not try a gimmick like adding a ridiculous second x to a name? If I see the second x, I assume low-rent, low-class.
The only exception is Jimmie Foxx, who was a solid hitter, and who clearly didn't choose to add the second x.