I think it would be nice if magma staves did fire damage, naturalist staves nature, acidic staves acid(duh) and so on.
In cases where more than one element is applicable(such as double egoes or say, infernal, which raises both blight and fire damage), it could pick randomly or go with the more important ego.
This would just 'make sense' to me and ensure there are no silly things like a magma staff which does cold damage