Take Visions can "destroy an object's ability to affect hearing"
1.1 Can it affect the ability of a PERSON or ANIMAL of affecting hearing?
1.2 A gruagach casts a spell on a magus, making the magus "unable to affect hearing", Can the magus use Voice range spells? (Edited for clarity)
Likely answer is "no" to both, but just to be sure. However, Cloak for the Thief of the Night seems to imply that it can affect PEOPLE (not just objects) and leave them unable to produce sound (spell description; it does just that), so it might be that the answer is "yes" and it can be used as a magical shutdown effect. For traditions like Gruagachan that is a terrible thing since they rely in their voice to work their magic (except Personal spells).
How long do you need (in your sagas) need to have the Visions flaw on "active mode" to produce something meaningful? Instant? Diameter? Sun? Moon?... Forever?
Would you determine that having claws of a wildcat (bonus to brawl, let's say equal to a dagger, and bonus to climb) is a minor or major improvement/ability? And gaining the running speed of a stag?
1.2 I'm not sure what you are asking if it is about someone who is deaf then yes he still can be affected by voice Range as you i.e can shater stones at voice range and they clearly cant hear.
If it about someone who can't hear want to cast a spell but is still able to speak I would give a penalty of -2 on his spell casting because his ability to speak clear is affected from it but his voice range wont be affected.
Ah, will rephrase it, since you are quite right it is not clear.
I mean this: the gruagach casts the spell on a magus (or another gruagach). Since they are unable to affect hearing, does that mean that they cannot cast voice range spells anymore? Since their voice (or any other sound, for that matter) does not project beyond their own person. Basically, if having this spell cast on you mans that you are effectively Mute for the duration of the spell.
But a gruagach's voice spells are different. They are not following the Hermatic Theory They can effect people who hear the gruagach's voice but the gruagach does not perceive. IIRC, a target of a curse must hear it but the gruagach does not have to see them.
So what your asking is can a Take Vision spell make a target Mute or at least inaudible. My knee jerk reaction without grabbing my books is Yes. Such a spell sounds right up those cursing little Picts alley, and I think take vision is a workable if odd fit.