i know this might be funny but cool make shields deal the damage that they shield against example: dread skelly would do shadow and normal ps this is only on shield bash this is to make it more popular
shield bash should do more damage for the same reason as the top suggestion
Making them deal what they defend against is silly, because only constructs and beasts would be weak offensively and defensively. Having to lose out on offense or defense just because of a shield's typing, rather than its design, is pretty lame.