I don't understand how you can say that you can't target an image with a Magic Missle.
So in your land, what the heck happens if I try to cast Magic Missle at a rock? In MY world, a magic missle streaks from my hand, and then hits the rock, causing no effect.
I have a major problem with this interpretation of both Mirror Image and Magic Missle. Mirror Image doesn't DEVIATE anything, it just creates duplicates. It doesn't RANDOMIZE what image you attack. If it did, why the heck would it have that effect on a Magic Missle, but not on an arrow?
And just because Magic Missle's "target" is listed as a creature doesn't mean you can't cast it at other things (at least in MY world).
Magic Missle creates a magical energy missle which unerringly strikes its target. If the target happens to be a creature, then the missle does 1d4+1 points of damage, otherwise, it doesn't affect any "non-creature" target.
Thus, you can cast it at a rock, but all you get is a fancy light show, and not even a scortch mark on a rock.
If you want to say that spells automatically "fizzle" if they don't target something appropriate, that just screws up targets and illusions in general. You'd instantly know ANY illusion was an illusion, just by targetting it with a spell such as MM, and that seems REALLY bad in my view. You want to say that Magic Missle fizzles when you try to cast it at a Major Image, for example??