The MagAdjust of this game is just the damage listed that corresponds to the type of spell being cast, i.e. magic for sorceries, dark for hexes, and so forth. You'll notice on staves that some of them have equal magic and dark damage and some of them are weighted more heavily toward one than the other. The same is true for chimes. That helps you know if the item is better for sorceries, hexes, miracles, or a combination of 2 or 3 of them.
As far as what actually goes into the damage itself, it is a combination of the base damage as mentioned above, your INT and/or FAI depending on which school you are casting, and of course any reinforcements (+1 to +10) you've done to your staff/chime. Additionally, if you infuse Faintstone/Darkstone/etc to your staff/chime, you can add even more damage to the type of spell that applies to the type of spell you are trying to cast. That means you can make a staff weighted toward sorceries even more toward sorceries or you can more evenly weight it toward sorceries and hexes.
As far as wearables go, there are pieces of armor/rings that:
- Increase casting speed
- Give extra attunement slots
- Raise your INT and/or FAI by 1-5 points
- Give you more castings at the cost of HP
I don't know of any items that straight up give you raw spell damage like the Oolacile crown did in Dark Souls 1, but the +INT items definitely make a difference.
Ultimately, they've made your catalyst operate a lot more like a "normal" weapon in Dark Souls II. Just look at the damage number for the type of spell you are trying to cast. Also, pay attention to how well they scale for a given stat just like you would for any weapon. If there is an S under the INT picture on the screen for scaling, it will eventually do more damage than a similar staff with an A for scaling even if it started with less base damage.
Yes, upgrading your charm affects the potency of miracles. This means that the damage of miracles such as Lightning Spear increase and the healing of miracles such as Heal also increases.
It's more effective to upgrade your charm than it is to add 1 point into Faith. Upgrading your charm once will add 20-40 damage to your Lightning Spear which is significantly more than adding 1 point into Faith.
In short; upgrade your charm to increase miracle potency
(Upgrading your charm also increases the melee attack if you are so inclined to bonk someone over the head with it)
To reflect the queries in the comments, I have tested the healing and it does increase the amount healed.
Best Answer
Your dark damage scaling is determined by the lower of your Faith and Intelligence stats. So, you would have to increase your intelligence first to increase your dark scaling.
As for the Chime, reinforcing it would also increase the dark damage it does.
Source: http://darksouls.wikia.com/wiki/Dark