Why do most people consider wand wizards to be the weakest of the lot?
A +2 or +3 bonus (+4 or +5 at higher levels), once per encounter essentially turns one miss into a hit per encounter. At paragon levels and higher, as more encounter and daily powers are flying around (and the bonus gets larger), this bonus is even more valuable.
Several issues:
1) It uses Dex. This adds to a few skills and initiative, but it does nothing for Fort Defense or Will Defense. The other two implement types help balance out the PC defensively.
2) Second, the bonus does not turn one miss into a hit per encounter. It does this 10% to 25% of the time (using your numbers) or one encounter in ten to one encounter in four. If a player wants his Wizard to hit more often, he's better off upping his starting Int to 19 or 20. Granted, he could take Wand Wizard and start out with a 20 Int, but that's only Dex 14 max anyway (unless there is a Dex/Int race somewhere). Like other bonuses in the game system (unless stated otherwise), the player has to inform the DM ahead of time that he will be using the ability to apply the bonus to a specific attack roll.
Mengu said:You have no control over when that +3 from action surge will have an effect. You might be wasting it on rolls that would have hit anyway, or rolls that had no chance of hitting. However you know when wand of accuracy will turn a near miss into a hit. Plus by paragon tier, you can have a dexterity much better than a +3.
You don't know this. Where did you get this? It's not in the rules or in the errata.
It might be a nice house rule to allow the player to see his attack roll first (strong), or to even know if Wand of Accuracy is going to result in a hit or not (even stronger), but there are no such rules.