High ranks of spells are more powerful, either with added damage/buffage, increased duration, decreased casting time, or some combination etc. etc. blah blah.
In some cases (such as the fireball
line of spells for the mage) the casting time actually increases as the ranks go higher (for balance reasons of course.) Browse through the spell/ability lists for the classes
and you'll see that each new rank of a spell is the same spell/ability effect, but with increased efficiency/power/what have you. Or something. Hope that explained it.
Jaef -- 60 Hunter -- Crushridge
Shiesty -- 60 Warrior -- Crushridge