I am nostalgic but I miss the good ole D&D spell books for the different schools of magic.  The 8 different types you could take as a generalist or specialize and be better at some but unable to cast other.  Elemental does this to an extent with the elements but there is no way to create opposition books currently for increased bonus unless you create a specific path, which people are doing I think, that restricts spells to be only on that path.  Example, someone takes Path of the Mage at level 2 and unlocks certain general spells, at level 4 you can choose to be a specific elemental mage or a generalist.  Specific path mages get access to increased power from their specialty as well as a unique path spell for each tier.  A generalist would get access to all but the unique spells and get access to the meta magic spells, more than one element spells, this is possibly more complicated than what you are suggesting, or simpler not sure.  But hope this helps.

My 2 Copper.

I would approach this as adding spellbooks to the game. Sure, the core books could use some extra options. But we don't want too much power at each level. Instead of just adding some stuff to the elemental spellbooks, why not add more spells in a new kind of book, like the flesh bound tome? One book I am working on is based in alteration magic. Things like levitation, burden, feather and other physical changes to the world are added. The book will be available as a technology unlock in the magic tree. I might have something like Sorcery unlock the option for Path of the Mage at level 5 for instance. That kind of content addition fits very well into anyone's mod.

Thank you for the feedback all. Following your advice, i defineately think a modular approach would be best so that people can easily use only the spells they want.

I can easily see how too many summoning spells would be bad, i'm spending until mondy poking through the xml to see more closely how everything is pulled together. I've got some fun ideas that twist around some game concepts based off the collection of spells and quests that already exist.

also, my daughter wants me to mod an assassin bunny into the game based off of one of her stuffed animals. Should be interesting if I can make it work.