First I'm sorry but I have to point it out...
can sum mom
I'm not a pro linguist, but come on 
Moving on,
Your first point, although I agree with what you say partially it has to be trend lightly. Since increasing the AOE of a spell might render a subsequent spell irrelevant. For example, if lightning bolt could increase it's AOE, it would a bit become chain lightning.
After a while a caster will stop casting flame dart and move on to Fireball, and so on. And I thin it would make sense that another mage of higher level would cast the "same" fireball spell and make more damage.
On your second point, Although I wouldn't be super hot about combining actual spells with other spells, I think you are onto something there. If someone would have fire & earth spells, maybe have access to special tier of spells only available with both those spell books are picked on start.
Should the second point be considered, it would increase the need to have some restriction/bonus system in place about picking more than 1 spellbook.
Cheers,
V