Any kind of 'buffing' to INT will never happen, unless formulas get revamped. Many, MANY spells have some sort of Int/Level value figured in, as far as I'm aware, Shiris has kept the exact formulas a secret. >_>
Also, at some level, any % bonus given to damage would easily become outrageous.
I agree with effects that cause some effect, but that really sounds like you guys want to play Poke/FF - Quest.
Anyway, good idea, but there will have to be plenty of balancing work done before it could be implemented, I think.
The buffing to INT thing is right.
If you kept the % small, it wouldn't get too bad. By small I mean like between 1%-3%.
As far as the Poke/FF thing goes. Quest would still be unique in many ways. It's just spells are boring, plain and simple. You always know what's coming next.