The amulets of holding, silence and healing invoked all give +1 to Strength. But only to wizards and warlocks as far as I can tell. And probably to the Zen Masters, but haven't confirmed this.
To recharge an amulet, just sell it and buy it back. Am not sure if you have to be in the magic shop for this, so save first to find out.
If you don't have ID, you might save first before invoking anything to find out what it does. Then reload if you want to give whatever boost it provides to the character that needs it most, of the ones it will affect.