Hello Sike,
The example on page 30 is correct. The
Lightning +2 trait on Brogan (the defender of the attack) will increase both the
# of attack dice and
add to the effect die roll for the Hydra's Circle of Lightning damage barrier attack. This is in line with what Gewar was saying.
Your example of Samandriel's attack on page 24 is a good one Sike. This is the only place where we clearly state that attacks which have a modifier vs. certain creature types or traits also modify the effect roll.
The rule is this: All traits ONLY modify the number of attack dice rolled, except for spells or traits which specifically say they modify the effect die roll. Those include:
1) A few spells such as Temple of Light.
2) The Tough trait (it specifically says it modifies only the effect die roll).
3) Damage Type Modifiers (such as Flame +2 or Lightning -2).
4) Attacks which have a bonus vs. certain creature types or traits (such as +2 vs. Flying, +1 vs, Incorporeal, or +1 vs. Dark). These are always written in the attack bar and expressed as "+ X vs. Y". Essentially, treat these just like a damage type modifier.
In our upcoming FAQ we intend to make this much clearer, and include a simple chart similar to the one below.
What's interesting is that we were originally going to do away with all of these traits and instead just print simple symbols on the card graphically showing the modifier with the dice icon. So, a lightning +2 would show a lightning damage icon with a red dice with +2 on it, and a yellow die with +2 on it. Maybe we should have gone that route...
[attachment=145]dicemodifiers.jpg[/attachment]