Slight to reasonable upgrades in the lineup are great, but the A's team as constituted is not going to give opposing pitchers any nightmares. Like the Giants and Padres of yesteryear, ultimately the A's will go about as far as their rotation will take them.
Early on, Oakland made a clear attempt to add a starting pitcher when they posted $19M and then offered a four-year deal to Hisashi Iwakuma. That fell through and since then we've heard nothing in regards to adding a starting pitcher, even though with that $19M back in the A's account and Adrian Beltre still unsigned, the A's have the money available to made a serious bid at a useful addition.
The A's rotation is neither as certain, nor as deep, as it may appear. Anderson's health and Cahill's true skill level head the list of question marks, followed by the fact that Gio Gonzalez isn't road-tested like, say, Danny Haren and Jered Weaver are, and Dallas Braden seems to come up with one bizarre injury for each toe -- luckily that's only 8 bizarre injuries.
As for the depth chart, it looks roughly like this at the moment:
6. Outman (if all goes smoothly)
7. Ross (if back healthy)
9. Harden (if necessary)
Sliding a solid middle of the rotation SP into the #3 slot or so would go a long way to making the A's rotation "very good, period," instead of "potentially very good."
My #1 target going into the off-season was Brandon Webb, who could provide the ideal role model for junior protegé Trevor Cahill and whose value is lowered by the fact that he hasn't pitched for the better part of two seasons. Webb has recently been linked to 3 teams, including division rival Texas, but the A's are not among them. It's unlikely that Webb will sign a deal that would be prohibitive to Oakland's current payroll. (Edit: However, this recent report suggests the A's may have good reason to stay away.)
Among starters still available, Carl Pavano is the best but not necessarily the best deal, as he is seeking a multi-year commitment that comes with the promise of his Twins performance but the risk of his Yankees performance. I can understand the A's reluctance to consider Pavano, though his addition would immediately solidify a rotation that is currently high in potential but also aboard the midnight Regression Express to Meanland.
Now maybe the A's thinking is that until Beltre signs they want to keep enough payroll clear to sign him. Though it's worth noting that since Oakland pulled its 5 year, $64M offer weeks ago and said "We're moving on," we have heard nothing to suggest that the A's have changed their mind. We hear a lot -- whether true or false, inside dope or baseless conjecture -- about how Beltre doesn't want to sign with the A's, but not much about how the A's don't want to sign Beltre. IF the A's have truly moved on from Beltre, why haven't they moved on towards a middle of the rotation SP?
Or do they figure that to be Justin Duchscherer, the Cat in the Hat who keeps coming back, the man with more encores than "er"s? The beauty of Duchscherer is that his presence would allow Josh Outman some time to air out his rebuilt elbow in AAA, ready to slide in whenever the need arises.
My point remains: One way or the other, the A's need to add a quality starting pitcher to mix if they possibly can, because as "good but ideally not finished" as the upgraded lineup is, the same can be said of the rotation.