How much depth is enough for the St. Louis Cardinals?

I've got another few weeks of teaching left, which is probably the most concise explanation for my inability to remember that I write the front page post on Saturdays now. There's another animated GIF post due out later this afternoon, but in the meantime I have a question that I think we've been grasping at over the last two days, in our discussions of Tony Cruz's backups and what Ryan Jackson did to deserve Pete Kozma: For the St. Louis Cardinals, reasonably wealthy perennial contenders, how much depth is enough depth?

Matt Adams sits on one end, I think, as "too much" depth; in that same pitcher's park we were using to shield Ryan Jackson Adams hit .329/.362/.624, which, combined with his not-quite-average MLB debut, makes him look somewhat overqualified for a 24-year-old first baseman who will probably spend most of his time in the PCL or on the bench. In the near-term he's almost inevitably stuck behind Oscar Taveras for Carlos Beltran's job, and Matt Holliday and Allen Craig are both as likely as anybody on the team to be around at least through 2016, when Craig becomes a free agent.

Then around the lineup there's various permutations of depth—the middle infield, where nobody's quite young (Furcal) or old (Wong) enough to count as dependable depth this April; third base, where Matt Carpenter and David Freese seem nearly identical; et cetera—ending with catcher, where the gaps between MVP-nominated Yadier Molina, his backup, and his backup's backup seem so worrying.

At what point, then, do the Cardinals go from overqualified to just-qualified-enough on their way to hoping that Cody Stanley is ready? That is, when do they have the amount of depth that you'd expect a competitive and not-entirely-free-agency-driven major league team to have?

For me, at least, the question is very dependent on what the player sitting atop all that depth looks like. As I said yesterday, if the Cardinals' MIF starters weren't alternately injury prone and not very good, a middle-of-the-road prospect like Ryan Jackson would be almost perfectly cromulent sitting behind them. Divorced from context, I think he's my answer to this question: "Enough" depth for a team like this, assuming the starter can be counted on to play 140 games, is Ryan Jackson, a 25-year-old kind-of-prospect with enough skills that he'll probably escape replacement level but enough questions that he won't be installed as a starter on purpose.