What I find alluring about the idea of moving Andrew Bailey into the starting rotation is that no matter what your opinion, there are quite a few arguments to be made either way. I thought I'd try to itemize them here, as the basis for further discussion.
Of course the big unknown is how Bailey would actually fare in a big league rotation, but for purposes of this post I am going to project him, best-guess style, to be a "solid #3." I am figuring that as a starter Bailey would bring a low-90s fastball, excellent cutter, use his curve a bit more, and throw a lot of strikes early and often. He would likely be a lot better than he was as a minor league starter, due to increased confidence and maturity, but would also not be as good as he has looked closing this year -- because let's face it, just as Ziggy could not keep up his 2008 pace forever we have to be seeing the best of Bailey in any role. But a solid #3, a pitcher who could go about 12-9 with a 3.80 ERA? Seems reasonable, neither too ambitious nor too conservative. So let's say these are the choices: A solid closer or a solid #3 starter...
1. Research simply shows a good starter to be more valuable than a good reliever. Good starters are harder to find, good relievers easier to replace, good starters able to throw more innings and thus help you more of the time.
2. With his control, fastball command, and his "swing and miss" cutter and curve, Bailey has every bit the repertoire to succeed as a starter even if his fastball velocity dropped a tad due to the pitch-load of starting.
3. The A's are not so deep in pitching right now that a #3 starter would be anything but a key addition to the mix. There is absolutely no guarantee that Cahill or Gio or Mazzaro is about to pitch at a level beyond a #4 starter in 2010, no guarantee Outman will pitch in 2010 or be healthy thereafter, and hoping that Anderson and Braden will perform at #2 starter level or better is being optimistic -- even if plausible. Make no mistake about it: Whether it's Bailey or someone else, if the A's can add a solid #3 starter for 2010, even for 2011, they will absolutely want to. You can never have too much good starting pitching and the A's are no exception -- not now, not next year, not in 2011.
4. The A's appear to have the bullpen depth to thrive without Bailey -- especially if his departure from the bullpen meant another good starter in the mix. Devine, Ziegler, Wuertz, Breslow, and Blevins can all potentially pitch in high leverage situations, the A's have consistently been able to identify and add at least one key reliever to the mix each off-season, and more promising options are knocking on the door with Gray, H-Rod, and Demel ready to compete for notice.
You can make a good case.
1. The only data on Bailey as a starter, from the minor leagues, is negative. To hear it from Bailey, much of the problem was mental (focus, etc.), and while it's hard to say whether the addition of the cutter, and now his major league success, might get him over the hump, the fact is that mental challenges are highly self-fulfilling prophecies.
2. Why mess with success? Here's a pitcher who has thrived in a role, plus your current ptions to replace him are a pitcher coming off of Tommy John surgery (Devine), a reliever who is not especially well suited to closing (Ziegler), and a reliever who has no real track record closing (Wuertz). And you want to lose depth in the bullpen in the name of making the middle of the rotation stronger? For an ace starter, sure, but a "solid #3"? Maybe just not worth it.
3. The bullpen isn't that deep. Devine is a question mark, Wuertz is an elbow injury waiting to happen, and the other relievers in the mix may be good but they're hardly great. You may lose more than you think when you pluck the best reliever out of the equation entirely.
You can make a good case.