Spell Damage & Why It's Not Very Good
Spell Damage is arguably one of the most misleading stats that you come across in Everquest. The reason for this isn't because of something that Spell Damage says but rather what it doesn't say. In almost every MMORPG Spell Damage is one of the most important things for casters to focus on in order to increase their damage.
In Everquest however this isn't the case. Spell Damage in EQ does barely anything to increase your damage and it's very quickly provable by doing the math of any spell you commonly use. Below is the math involved in calculating how much bonus damage spell damage actually grants you. You can google the equasion if you'd like, I got this one off of the Everquest wikia.
(Cast_Time + Recast_Time) / 7 * Spell_Damage = bonus damage per hit of spell
BASE Cast Time + BASE Recast Time divided by 7 and multiplied by your current spell damage.
The spell, Spear of Molten Shieldstone Rk. II will be what we use to demonstrate how much damage will be gained from 843 Spell Damage. Below is a screenshot of the ability using MQ2 Tooltips to give us more information about the spell.
As you can see the cast time of the ability is 3.5 seconds and the recast time of the ability is 9 seconds. That would be a total of 12.5 seconds. Now we need to take 12.5 and divide it by 7 which the result ends up being 1.7. The final step of this math problem is to take the number we just got and to multiply it by the total amount of Spell Damage that we have; 843.
The final number we get is 1433.1. Now it's very important to state that this is how much is added total AFTER your cast - this number is not added to your 'base damage' and then multiplied based on how much you crit for. No, that would actually make it good and worth focusing on. This is a total of 1433 damage over all on your entire cast.
Is Spell Damage worth getting? Yes.
Is Spell Damage worth FOCUSING on getting? No.
You shouldn't use Spell Damage as a judge when choosing a new piece of gear and you shouldn't go out of your way trying to get more of it. There's always going to be something that's more useful for you to get than Spell Damage (like health, get health you can never go wrong with too much health).