Yes. Which is why you shouldn't give + to your Kamihime. You either give the stats to one Kamihime, which gets multiplied, or you give them all of your party, which gets multiplied.
As for what to do with your weapon +1 fodder, well... if you're a perfectionist, wait until you get your hands on a LMB Assault SSR weapon. You can combine it all into one item and then throw that one when you finally get a weapon that's sure to stay equipped practically forever.