The substantive scope of the state secrets privilege and the question of who decides

Over at Concurring Opinions, Gerard Magliocca notes the Supreme Court’s cert. grant in the General Dynamics/Boeing state secrets case (arising out of the cancellation of the A-12 contract).  With all respect, I think he is mistaken about two points in his post.  Both have to do with the issue of what information ought to be protected by the privilege in the first place. 
First, Gerard suggests that the A-12 case “may not lead to a clear ruling on the merits or on the scope of that privilege, but that question is now on the table.” I don't think I'd agree, assuming Gerard means that the Court might in this case address whether the privilege was properly invoked or might otherwise address the scope of information properly said to be privileged.  As I note here, the petitioners in this litigation at this point do not challenge the merits of the government’s privilege assertion, but rather object to the consequences of its invocation in this instance: i.e., the proposition that the government can advance a contract claim against them while using the privilege to preclude them from raising a defense.  As to the merits of the underlying invocation: the secret information at issue concerns stealth aviation technology, which strikes me as more or less a paradigm case of a proper invocation.  [UPDATE: Gerard and I have corresponded about this, and I now appreciate that he merely meant to say that the case is an occasion for a larger discussion about the scope of the privilege, not that the issue will likely come up in the litigation itself.]
Second, and more significantly, Gerard suggests that the privilege is “not reviewable by courts,” comparing it to such (arguably) non-justiciable issues as habeas suspensions or declarations regarding a state’s lack of a republican form of government.  I know this is often said about the privilege (i.e., that judges must go along if the executive branch invokes the privilege), but it is not so.
When the government litigated the seminal Reynolds case in the early 1950s, it expressly advanced this view, arguing that judges should give binding deference to the executive official’s claim that the privilege should attach to the information in question.  But though the Court ultimately agreed with the government that the privilege was applicable in that case, it expressly rejected the proposition that courts have no ability to reject the executive official’s privilege invocation: “The court itself must determine whether the circumstances are appropriate for the claim of privilege,” the majority held.  To be sure, the majority then went on to state that courts should be reluctant to actually require production to the court of the secret at issue—by way of illustration, consider whether you would need to actual see the engineering details of stealth designs in order to conclude that those details are protected by the privilege—and it inappropriately assumed that in that particular case there was no need to determine firsthand whether the document in question actually contained the supposedly-secret information at issue (as it turned out, it did not).  And it also is true that judges in actual practice routinely state in their opinions that they give “great” or “substantial” weight to the expert judgment of the agency heads who invoke the privilege (see here for a discussion of the theoretical dilemmas this involves). In the final analysis, however, the current doctrine does not call for the judge to act as a rubber stamp.  No judge in the post-Reynolds era, so far as I am aware, has simply accepted the executive’s invocation as conclusive.
The real question as to merits determinations, then, is whether it is realistic to expect judges to second-guess the agency head even if the doctrine in theory permits him or her to do so.  That is, is the formal capacity to reject the invocation merely window-dressing, masking a reality of binding deference in practice?  And if one thinks this is so, what reforms might make sense?  One option is to try to more narrowly define the category of information substantively eligible for protection.  That strikes me as unlikely to work.  Another option is to alter the process of litigating the privilege, as seen for example in legislative proposals that would allow either for a stand-by counsel or even the party’s own counsel to have access to the secret information in order to directly contest the privilege invocation (the status quo involves an ex parte, in camera determination).  I think there is something to be said for the stand-by counsel idea, assuming one can develop an appropriately-cleared corps of attorneys suitable to the task.  I’m much less keen on proposals to allow the party’s own attorneys to have the access.  But in any event, whether to pursue such changes in the first place requires one to make the case that the status quo involves excessive deference in actual practice.  I don't think that case has been made (please note that this issue is distinct from the sharp controversy as to whether the privilege should still attach where the secret information involves illegality).