Oof. Good luck. Myself, I run only low-level games, so, de facto, I ban many spells. One time, for a game with some intrigue, I banned detection spells; this really made players upset. Anyway, one guess is that your GM is banning spells because he doesn't know how to deal with them; pretty reasonable, since GMs have to be concerned with a far greater breadth of material than players.
One random thought is that since you're playing in a combat-heavy adventure, is to have players switch off characters and opponents. The GM can either have his turn at playing a hero, or sit back and "direct" a scene, with one of the players playing the bad guys. GMs don't like to lose battles, either, and this takes off the pressure of constantly creating a "beatable challenge" for the party.
Cedric.
aka. Washu! ^O^