I also think the feat-for-item tradeoff would be unbalanced in favor of the feat. Not horribly insanely unbalanced, but yes unbalanced. Especially when you look over the lifetime of the PC, where the bonus to damage you're getting from the feat will scale up higher than any other bonus to damage granted by a feat (say from a +3/+4 staff at paragon where Weapon Focus is only giving +2, and a +5/+6 staff at epic vs +3 from Weapon Focus). And it's effectively an untyped bonus to boot!
In fact, even with two wands the feat seems pretty uber, but the opportunity cost of keeping that second item up to par is at least somewhat higher than the opportunity cost of a single feat. There may also be an opportunity cost to not having the off hand free for a different item (though it's not clear to me how it would work with the staff if allowed, perhaps you'd have to hold it in two hands as well?).