I have some questions about this specific spell, though it likely has wider game mechanic implications.
Damage: As described the various referenced damages (Staff +10, Branch +8, Wand +5) are all damage modifies (as opposed to damage itself).
If that is accurate, to what is the modifier being applied? The only explanation I could come up with is that you still effect combat rolls, but that does not seem to work. As the Spell automatically hits, why would you roll Attack. Also what would your attack stats be? Supppose you are untrained in combat, you'd have 3 botch die if you botch, but since you cannot miss what would this represent. Suppose your Attack roll was insufficient to overcome the defence of your opponent, this would mean you miss.
If therefore you do not roll Attack vs Defence, you just roll Damage, unless there is another element to the Damage, the Modifiers would not in fact be modifiers, but the actual damage.
Although the spell automatically hits, if a Magus wished to strike a particular part of person (say hit him in the eye) would you modify the spell's target to Part or roll Aim.
As I recall, all spells inflicting damage via a medium uses the +N notation.
See CrIg-spells for other examples.
To determine the actual damage caused, roll a stress die and add. See note on 'spell damage' p. 116 of ArM5.
This is soaked with soak total + stress die, as described on ArM5, p. 181
Discussed on page 181 of the main rule book under injuries. Damage is stress die +defined amount from the spell. Soak is stress die + appropriate soak modifiers.
The horn tail dragon breathes jets of fire at Harry for 35 damage, surely a killing roast. Harry narrowly dodges the attack by hiding behind a rock which soaks all the flame. I write that as a means of illustrating how one might describe surviving what would otherwise surely be a killing attack.
I wouldn't let attacks target a specific part of the body unless it were designed that way and I would up the magnitude for complexity to compensate. Damage would be the same as the underlying spell.
Yes "non-combat" only means "not involving waving weapons around hoping to ht the enemy" rather than "not in a combat situation".
All forms of damage in ArM involves one die roll and all soaks one roll.
In combat - meaning involving melee or missiles etc. - the die roll is for Attack for the offender and Defence for the defender, Attack Advantage plus Damage modifier minus Soak.
When throwing around spells and such it is Damage+Stress die versus Soak+Stress die.
This is incorrect because it leaves out the possibilities that violate the general rule, and they can show up quite often. This would be correct if aimed spells used Attack Advantage, but they do not. Aimed spells have a roll to hit followed by another for damage, and the defender also makes two rolls. This was one of the reasons I thought aimed spells should use Attack Advantage. But David has said the intent is for aimed spells not to use Attack Advantage.