well first of all balance won't come only from editing spells and their values, you must have balanced item stats for each class, to know how they scale with different stats, what coefficient to use on items because 1 intellect != 1 str and 1 str != 1 agility you must have this thing balanced first, armor , parry , dodges, spell power, attack power, haste , hit, crit etc.
That would be first step.
Second step after you did that with item stats, you have to move to weapon stats , again here 1 weapon damage != 1 spel power for casters nope it's not like that, you have to find it by yourself, depending on first step which class/type of characters missing damage or do to much of it, if for example casters do a bit to much damage don't add tons of spell power here, try to mix with secondary stats, if melee classes wrecking even with shitty weapon, don't put to much of weapon damage , also take a note about weapon speed it's quite important.
Third Step nerf,buff talents if you running 255 server there is plenty of talents that over scaled , there is one in mage talent tree that gives armor from intellect, one in paladin protection tree that gives strength from intellect i think.
Forth step.After you solved all talent problems. you can start editing
Spell_bonus_data on spells that still do to low damage, for example that will be rend, shaman shocks (i know that from my experience). in the end of these steps you should have pretty much balanced server.
But take a note here, balancing is not made by editors or such it's made on players testing each spell, class item etc, and one more.
P.s you can't balance server if you never played in retail / blizzlike long enough and you don't feel how stats affecting each class and how they scale from stats.
Good luck with that, server balancing is one of the most important things, and one of hardest.
Best regards ,Vitrex.