How about instead, make it the wizard equivalent of the fighter bonus, which imo would make sense...
Wand of Accuracy: Spells you cast through your wand are more likely to hit their target. You gain a +1 bonus to attack rolls made with powers including the implement keyword while channeling your spell through the wand. Once per encounter, as a free action, you may alter the result of a die roll by an amount equal to your dex bonus. This alteration can be made after the result of the die roll is known, but before damage is assigned.
how is that?
+1 to hit is much more powerful than +1 AC, especially for a class that often targets many creatures when it attacks.
I think that simply allowing the wand to effect every target of a power would make it more in line with the other choices.