Focus on adding new abilities like summoning abilities, malus and bonus spells, ect...
I didn't dabble a whole lot in abilities as of yet. Maybe, if we do indeed add an Undead race as mentioned in the New Race forum, perhaps we could have racial spells that only affect the opposite race.
For example, maybe the Undead get an ability which uses the corpses of the Humans to resurrect a ghoul. Then, the Humans have an ability which dispels all magical effects in an area, including these special ghouls.