The danger of a hex includes a wall of fire/moat; the presence of other creatures nearby in case they can be used as a shield against a burn, fireball, or area-of-effect attack by stepping onto the hex; and enemy stacks that a creature exposes itself to by stepping onto the hex.
The value of an attack includes the attack itself, the retaliation, the removal of retaliation, the burn, and the area-of-effect attack in both directions, the blocking of archers, and the danger of the hex that the creature steps onto.