Allow me to take issue with one presumed advantage you describe: the advantage of drawing from their own experience in marriage counseling. To some extent the potential (note potential)  for objectivity by the celibate counselor can be an advantage in pre- and post marriage counseling. Non-professional counselors (most clergy, I contend) tend to bring their biases to discussions. If one is a "directive" style one is simply stating the role, relationship and specific denominational obligations of marriage. If one is "non-directive" one is ensuring that the parties are informed and that it is effectively mediated between the parties so that they arrive at a mutual conclusion. So the criterion is professionalism not whether one is married or single. Who bases their selection of "pamphlet", psychologist, psychiatrist on the basis of marriage status?
That being said I admire your openness and agree with your final conclusion: choice.