Well, in any given set of at-wills there will always be one that is most powerful, so that is not a valid reason to do or not do anything. I think you might mean that even +1d4 + items + feats is overpowered, and I think that's not sound either.
As it currently stands, Magic Missile will do about half the damage of a normal At-Will, but hits automatically. Assuming you hit about half the time, that puts it on par with other At-Wills.
The previous version (and other At-Wills) are better in situations where you hit more often or are adding large damage bonuses. They are more capable of being optimized.
The new version is better in situations where you are hitting less often (blind, at penalties to hit, etc) or are weakened (which doesn't apply if you don't roll to hit), or have bonuses to damage from an enemy being vulnerable.
What is nice is this means you can have the new Magic Missile along with another normal Wizard At-Will, and can use whichever one is better for the situation. That's pretty cool.
If Magic Missile hit automatically but could get all normal bonuses to damage, it would be the strongest power in the game - or at least, most potentially abuseable. We don't need that. Avoiding having one power be blatantly stronger than others is
absolutely a valid reason for design!
As it is, it is neither stronger nor weaker than other At-Wills, but instead it is
different, which is very useful.