"Etheral Summoning" - Replace it with a new self-casting spell "Etheral Presence", which will apply the ethereal (Night Mother) shader, allow you to resist normal weapons for 100% (but be completely vulnerable to silver, deadric, and enchanted items, as well as magic, so it's not too powerful) and (if you want) disable collision so you can walk through units (not sure if you can exclude walls from such an ability). So basically, normal weapons go through you without harming you, and you can walk through units (again, not walls, as that would be entirely unbalancing). At higher levels, all of you opponents will use either enchanted, or daedric/silver items, or magic. So - what the sense of making your hero vulnerable to them?