I've read that some weapons have holy powers and do more damage against "dark enemies" (like PD and DF and creatures), like the Psycho Wand, Elsydeon and the Silver Tusk. I witnessed it myself since Rika does more damage against certain types of enemies using a Silver Tusk instead of a Guard Claw but I've never really compared the two (averaging and such). Does equipping Rika with the Silver Tusk and one Guard Claw do more damaged to PD than two Guard Claws?
I never ditched the Silver Tusk for nostalgic reasons anyway. And lately I always keep the Genocyber Claw and the Silver Tusk for Rika, since the Diem effect of the Genocyber Claw is nice as well, I only exchange that for a Guard Claw just before PD.