I think it must be because of the damage type of the spell, because I attacked in different ways and nothing happened.
Probably ... they are resistant, or even imune for some type of damages ...
If you click them with right button, choose "examine" (i think), and go all the way down in statistic ... you can find there complete list of types of damage they are either reistant, imune, or vulnerable.

They should either question why you are putting dangerous items with them, or attack, depending on each NPC's personality and your relationship with him.
In that case you get mine +1

(Its not like it means something around here, but still

)
Losing a spell slot to regain 100% health and the rest of the party slots, I think it seems profitable to me...
There is no block carry weight, there is send to camp.
The time to get things in the box is negligible.
Ad 1 - Nope, the deal is loosing either 2 or 4 spellslots now (not sure if you create one, or two godberries) ... so your party can regain 100% health, and all spellslots AFTER the fight is finished.

I dunno about you, but i get the feeling that especialy Land druid is conciderably weaker without his spellslots.

Ad 2 - I know, i mendioned it in third option.

Ad 3 - It depends on your personal preferences ... speaking for myself, i finded it tedious and anoying.
First, the use of magic pockets is automatic in some cases, such as opening doors for example.
Im aware ... i played the game (a lot actualy, probably more then i should).
And i like this, since it saves me time. :P
This is one of things i allways hated in Dragon Age: Origin ... when i clicked on locked chest, why the hells do i need to switch character, unlock the chest, and switch it back ... instead of my rogue simply step forward and unlock the damn chest. -_-
So honestly, i glad Larian came with this improvement. :P
Second, your argument is like, "I'm going to give a sword that does infinite damage to the player, if he's feeling bad, just don't use it".
Well, no ... my argument is more like "please try to understand that all changes you enforce will affect millions of other players, do you really need the thing gone so badly?" :-/
But even if, i would agree with such approach ... im all in for self moderation and free will ... if someone wants to deal infinite damage and ruin his game (in my eyes) its his choice, and honestly if he would have fun playing the game like this ... good for him.

The hag would simply think you are still a possible threat and continue fighting.
Well, you have the option by refusing her deal and finish her off. O_o
So, the ideal would be an impossible dream, which involves a lot of AI.
But being realistic, it could have basic and generic actions that could be applied in any situation, such as "leave/run", "attack", "cast a spell/scroll", "ask person X in the party to speak for you". Maybe a few more social interactions:
"threaten", "intimidate", "soothe", "frighten", etc.
I believe Swen was talking here that using spells during conversation is certainly something they are workin on ...
With that addition that if we will use spells during conversation, NPCs will notice.

Simmilar as if Kithrak is using Detect Thoughts on us and we can recognize the spell, if gods of dices are on our side.
Attack is mostly right there in bottom left corner (those crossed swords) ...
Switch controlled party member is right next to it (two circulating arrows) ... but sadly so far there is no way to switch speaker, but it was demanded multiple times.
About the rest ...
Im not quite sure if implementing them to all conversation is good idea, but i would certainly not mind if there will be more.