Opportunity cost.
If a character of mine ever made a Wizard use up a 2nd level spell slot in order to turn a miss into a hit, I'd smile. The wizard just used up an opportunity to cast Hold Person, Flaming Spehere, etc.
If a Wizard ever used up a 3rd-level slot, I'd celebrate. That's an 8d6 fireball that won't be coming at me.
Okay...except that he'd only be getting to level 3 slots in round 9. Against our longsword-wielding fighter friend, the wizard can spend round 1 flying up into the air, round 2 and 3 casting Disintergrate--with the first one maxed out for 100 damage against our fighter's -1 or +2 dex save--and then on round 4 drop power word kill.