Beyond the general buffs (intelligence, vitality, mana/arcane power), are the elemental damage bonuses (fire/cold/holy/etc.) tacked on to spells? Are any weapon effects flat-out useless for certain classes?
Elemental damage on weapons is factored on top of the base damage of the weapon. So for example, a weapon that does 5 to 10 damage with +2 poison damage actually does 7 to 12 damage - however it does not change the type of damage you do (bad source). So in essence, +elemental damage should be treated the same as +damage on a weapon, which translates into more damage to your spells.
Anything that raises you damage overall stat is good, attack speed obvioulsy sucks on cooldown spells but is good on spammable ones.. etc.. your main focus should be high dmg weapon + loads of int, attack speed is good on burst witch doctor setups but sucks on dots/pets setups.
This is not quite right. It might have been the case in a phase of the beta, but it changed for the final version. It is true, that the elemental damage is overridden by spells like Arcane Missile (Wizard - "... causing 110% weapon damage as Arcane"). Here the full damage done will be arcane. Just to make it clear, the elemental damage influences the damage of the spell, but the damage is not done as the original elemental damage.
But if there are spells like Bash (Barbarian), where nothing is written about doing damage as another type, the damage is done as the elemental damage, written on the weapon (scaled percentally).
But I'm wondering, if there's any benefit, except doing more damage to mobs with lower resistances of that damage type.
I was just running some tests on attackspeed and dots, and the TL;DR is that Attack Speed is a useless stat for dots.
I was able to add 25% attack speed between a ring and an amulet without effecting any other stats. I had no other bonus attackspeed, but I was wielding a pretty fast ceremonial knife to start with. I did all my testing on the Zombies outside Tristram in hell.
My stats, off the character sheet: Damage: 1273.63 Damage increased by intelligence: 870.00% Damage increased by skills: 0.00% attacks per second: 1.4 Critical Hit chance: 5.00% Critical hit Damage: +50.00%
Equipping my two attackspeed items changed: damage: 1592.04 Attacks per second: 1.75
First I checked locust swarm. I didn't record the order of ticks (which seemed random), only the number of ticks of different numbers.
Without attack speed I saw:
With attack speed I got:
Haunt was a little less clean. Most ticks were 213, but the increments were all still in multiples of 40, and it seemed like the extra 3 damage varies between the casts with different numbers of ticks. Without attackspeed I got:
Result: I'm nearly sure I just miscounted that one locusts (counting two different things while kiting even slow moving mobs is harder than it looks :/), and there's what looks like rounding error with the numbers out of haunt, but we were looking for a 25% damage increase, and it's just not there.