I'd like to be able to turn them on and off. Everything the OP suggested sounds cool.
Just as a development suggestion, the weapon could get a "gradient" around the center-point of the mode, so the handle would be frost, shock, fire free, while anything above it (namely the blade of the sword or wings of a bow) or below it would be plastered with the elements. Would make it s you wouldn't need to define designated visual areas.
I also hope spells with have varying visual intensity. Small spells would look weak, but a high powered frost, shock, or fire spell would cause a frost torrent, lightning bolt, or ifnerno.