I have a reflexive sympathy for the proposition that we shouldn't have secret courts giving secret interpretations of secret laws to secret agencies based on secret arguments. And I've been one of those fabled conservative-libertarian opponents of the PATRIOT Act basically since it was proposed. It was one of the principal reasons I got involved with the ACLU in college.
P.S. Miranda concerns are barking up the wrong tree. In fact, they're really in the wrong forest. Miranda was a Fifth Amendment decision (regarding the rights to due process and against self-incrimination). The principal constitutional concerns here are the First and (especially) Fourth Amendments. And, of course, the larger liberty concerns are related to the privacy of those not even under suspicion, not the procedural protections of those actually in custody.