In short, there are concerns that my statement:
"As a result, even the prayer of the most unknown of saints in heaven would have equal efficacy as the greatest saint".There is a worry that this downplays and even confuses the notion of why Catholics pay such high devotion to Mary. Why is anyone devoted to her in asking for her intercession, if her ability to intercede is not "greater" than everyone else? Didn't Mary's life on Earth establish her with this power?
I think a few ground rules need to be established before going any further. First and foremost, it is God, and God alone, who can answer prayer. The saints can only intercede. Their role in the answering of prayer is secondary in imploring their assistance, not primary.
It is for this reason that the Church has never taught that there are things that Mary can obtain that the other saints in heaven are incapable of doing on a strictly objective level. To the degree that this is believed, one runs the risk of having an improper devotion. Even our piety is imperfect, and it is something we all must deal with.
Finally, in heaven, there is no "better" or "worse" in heaven. Even still, intercession of the saints in heaven is not based on what the saints did. The ability to intercede is based upon what Christ did. To the extent we share in Christ's priesthood, we can intercede, for we are a "kingdom of priests." Those in heaven participate fully in Christ. Sin limits our ability to share in that priesthood. (For whatever you ask in my name shall be granted Our Lord tells us.) Those in heaven have no sin, being "the spirits of just men made perfect." We also know that since they are in heaven, Christ provides them with every need, so that they lack absolutely nothing, and can obtain whatever they ask in accordance with the Father's will. Of course, the saints cannot not do the Fathers will.
So why do we venerate the Virgin Mary with such high honors? In order to understand this, we must understand the first rule of what is called "Mariology", the theology behind devotion to Mary. mary is never honored by the Church for her own sake. She is always honored for the sake of Christ. When the Church proclaimed her Theotokos (Mother of God), they did so primarily to protect the proper understanding of Christ. Even with the Assumption of Mary, the Church holds that ultimately her being taken into heaven, while a singular grace, also foreshadows our eventual heavenly home by the power of Christ's Cross and Resurrection.
So we aren't devoted to Mary because of her powerful intercession. We are devoted to Mary ultimately because of she was because of Christ's saving power. Mary lived as we are called to live, freed from the dominion of sin. She was free from such dominion because she lacked original sin. Eventually, all of us will be like that in heaven. We will be freed completely from sin. In Mary, Christ gave a foreshadowing of that for us all. (Some Protestants may dispute this, but my point is not to go into the doctrinal questions regarding Mariology, only to for the moment show its purpose.)
This is why we honor Mary. In pondering her life (and in asking her intercession, we always are to ponder her), we learn how to live in full accordance with Christ. Pondering the lives of even the greatest of saints on this world, they still had sin, and hence there was some way they did not serve God perfectly. When we ponder Mary, we ponder how she fulfilled the will of her Divine son perfectly, since there was no such separation on account of sin. The saints in heaven are just as she is now. The only difference is she was that from the moment of her conception, to prepare her for the role of being the mother of Our Lord and Redeemer.