Dumbledore's death would probably be not worth the trouble right now, but I think that if it were possible Quirrell would have removed and impersonated him before Harry ever got to Hogwarts.

Quirrell probably has more raw talent than Albus, but when someone has an ancient wand that guarantees combat victory talent isn't enough. He's smart enough to know he'll need to plot his way to victory, because he is not beating the Elder Wand.