Carpenter was our best linebacker against Seattle. Inside or outside, expect big things from him this year.
But I certainly think that adding another top linebacker would not be a "waste." Greg Ellis is getting old, recovering from major surgery, and was never a prototype 3-4 OLB, even in his prime.
In Phillips' 3-4, all four linebackers need to be good blitzers, because you will get burned if they aren't. Often, blitzes are designed so that either the inside linebacker or a stunting outside linebacker will get a relatively clean shot at the QB. If they don't get there, then the defense will be horribly exposed.
By my count, we have three guys who can blitz and cover effectively: Ayodele, Carpenter, and Ware. Burnett has had trouble keeping weight on, and it's not clear if he can contribute as an everydown player. James has shown very little propensity for blitzing, and has been less than stellar in other facets of the game.