Falling Icicle
Adventurer
Keep in mind, to get ANY bonus from the second implement, he'd have to get the Dual Implement Wielder feat anyway, so it isn't appropriate to count that in the "cost" of this concept.
That said, sure it costs one feat to make the staff a double weapon, but for the price of that feat you're getting a "double the enhancement bonus of staves for damage rolls". Is that balanced with the usual requirement from users of the feat of having to buy an additional Implement to carry? I guess that will vary from DM to DM.
There are other advantages to wielding two implements, like getting the benefit of two properties and the potential use of two implement mastery features.