Ultimatecalibur
Explorer
Basically no spell should scale, but many spells should be able to be prepared at higher levels to gain a more improved version of the spell. Since this is what I think WoTC was going for, they need to rework Magic Missile so that it does not automatically scale. As a cantrip, it should fire one missile, just one. Perhaps as a first level spell it can fire multiple missiles (up to 3).
But Magic Missile is not a "Spell," it is a "Cantrip." As "Cantrips" are at-will magic, Magic Missile needs to be balanced as a (weak) at-will attack.