[Kuroshima]

Well, truth to be told Fireball'ing away is a losers proposition in RAW GURPS, so you opting for other spells is actually a smart move. Leave doing damage to those that don't need to expend resources to do so. Look for spells that disable an enemy directly, or that impose heavy penalties for your offensive arsenal. Look for buffs for the rest. Bless and Curse are both awesome. Curse in particular might not seem like much, but it's unresisted, and it will lower resistance to other spells, active defenses, etc. Don't dismiss the clause that says that a curse can be expended to turn success into failure for particularly significant rolls. What's more significant than failing a resistance roll or active defense against something that will take you out of the fight?

EDIT: of course if you want your GM to hate you, take delay, hang spell, and maintain spell. Then expend some time in the morning precasting your slow expensive spells, rest to recover the ST, and use them immediately in combat, with no energy expenditure. It's the fastest way to convince a GM to start houserulling Magic or to switch to another system.

Speaking of other magic systems, blasting wizards work much better under Sorcery than under GURPS Magic