For direct-damage spells, when the spellpower is increasing the damage, it is usually directly applied as a synergy. Thus, if your spellpower influence value (how I call it) is 63, your skill will be doing 63% more damage (for example 163-326 instead of 100-200).
The formulas depend on the character. They are:
Barbarian: 100 * spellpower / (spellpower+150)
Paladin, Amazon: 200 * spellpower / (spellpower+400)
Druid, Asassin: 400 * spellpower / (spellpower+900)
Necro, Sorceress: 800 * spellpower / (spellpower+1900)
The formulas are designed to result in 40 if you have spellpower 100. The Barb gets lower bonuses after and higher before, while the Sorc and other caster chars get more after and less before. This means that it still is good to invest in spellpower if you already have 300 spellpower for a Sorc, while for a Paladin or Barbarian it is about useless.
Here, a little table that shows the effect better I guess:
Code: Select all
Spellpower Barb Pal/Ama Druid/Assa Nec/Sorc
20 11 9 8 8
50 25 22 21 20
100 40 40 40 40
200 57 66 72 76
300 66 85 100 109
400 72 100 123 139
500 76 111 142 166
600 80 120 160 192