Having established in the OP that when Catholics (and Orthodox and Anglicans/Episcopalians) “pray” to Mary (and the Saints inheaven) they do not mean the same as whwn they “pray” to God ( parakaleo vs proseuchomai), I will move on the the main points in this discussion.
I intend to show how the Catholic practice of “praying to” Mary and the Saints is reasonable and scripturally valid. I want to make three propositions and demonstrate them from scripture.
1. We are encouraged to pray for others and to ask others for their prayers.
2. Mary and the Saints are validly included in that
3. They can intercede for us in heaven
Praying for others
There are dozens of examples of people praying for others in the Old Testament. For example
“The prophet Jeremiah said to them, “Very well: I am going to pray to the Lord your God as you request, and whatever the Lord answers you I will tell you.’” (Jer 42;4)
In one instance at least God specifically commands it.
After the Lord had spoken these words to Job, the Lord said to Eliphaz the Temanite: My wrath is kindled against you and against your two friends; for you have not spoken of me what is right, as my servant Job has. Now therefore take seven bulls and seven rams, and go to my servant Job, and offer up for yourselves a burnt offering; and my servant Job shall pray for you, for I will accept his prayer not to deal with you according to your folly; for you have not spoken of me what is right, as my servant Job has done.” So Eliphaz the Temanite and Bildad the Shuhite and Zophar the Naamathite went and did what the Lord had told them; and the Lord accepted Job’s prayer. (Job 42 :8-9).
Now examples from the New Testament of asking others to pray for us.
"Pray also for me, so that when I speak, a message may be given to me to make known with boldness the mystery of the gospel, for which I am an ambassador in chains. Pray that I may declare it boldly, as I must speak." (Eph 6:19-20)
"At the same time pray for us as well....." (Col 4:3)
"Beloved, pray for us." (1Thess 5:25)
"Finally, brothers and sister, pray for us....." (2 Thess 3:1)
“Pray for us; we are sure that we have a clear conscience, desiring to act honourably in all things.” (Heb 13:18)
Others includes Mary and the Saints
This comes from the concept of the “communion of saints”. We believe Mary and the Saints are as alive and available to us as anyone still on this earth. We believe that those who have gone before us into heaven are one with us. They are all part of the one body of which Christ is the head.
“For just as the body is one and has many members, and all the members of the body, though many, are one body, so it is with Christ. For in the one Spirit we were all baptized into one body—Jews or Greeks, slaves or free—and we were all made to drink of one Spirit.” (1 Cor 12:12-13)
When they died to this life they did not cease to exist, their souls did not cease to be one with Christ, to be part of his body.
Jesus said: “..whoever lives and believes in me shall never die. Do you believe this?" (Jn 11:26). Therefore those who truly believe in Jesus never die. They are still part of His body. Jesus does not have a body with dead bits in it.
Consider this text also
“For I am convinced that neither death, nor life, nor angels, nor rulers, nor things present, nor things to come, nor powers, nor height, nor depth, nor anything else in all creation, will be able to separate us from the love of God in Christ Jesus our Lord.” (Rom 8:38-39)
Look at this another way. Jesus uses the image of the vine, with us as the branches.
“Abide in me as I abide in you. Just as the branch cannot bear fruit by itself unless it abides in the vine, neither can you unless you abide in me. I am the vine, you are the branches. Those who abide in me and I in them bear much fruit, because apart from me you can do nothing. Whoever does not abide in me is thrown away like a branch and withers; such branches are gathered, thrown into the fire, and burned. If you abide in me, and my words abide in you, ask for whatever you wish, and it will be done for you.” (John 15:4-7)
Are those saints who die cut off from Christ and thrown into the fire? Or are they still abiding in Christ and still bearing much fruit? Is Jesus still doing for them whatever they ask?
The writer of Hebrews uses the image of running a race with those who have gone before us cheering us on. “Therefore, since we are surrounded by so great a cloud of witnesses, let us also lay aside every weight and the sin that clings so closely, and let us run with perseverance the race that is set before us.” (Heb 12:1).
This follows his recalling of the heroes of the Old Testament and says about them “Yet all these, though they were commended for their faith, did not receive what was promised, since God had provided something better so that they would not, apart from us, be made perfect.” (Heb 11:39-40).
So they are alive witnessing us in our struggles. But they did not immediately receive what was promised, they had to wait for “something better so that they would not, apart from us, be made perfect.” So it follows that the Saints are alive with them, having been made perfect.
They can intercede for us in heaven
God is logical. That is evident just looking at creation. Now what do the scriptures say Jesus is doing in heaven?
“… he is for ever to intercede for all who come to God through him.” (Heb 7:25).
Now, we, on earth, are to be imitating him, what he did while on earth.
“Be imitators of me, as I am of Christ.” (1Cor 11;1)
Why would we stop imitating Jesus just because we go to heaven? Why would we sit around and twiddle our thumbs while our Lord and King is interceding for those on earth?
Does our service to our Lord end when we go to heaven?
Or is the body doing what the Head is doing?
Now Mary and the Saints are mighty prayer warriors. Think about it. Are they hindered by such things as human failings and needs (such as sleep)? Those in heaven have no hindrances of such a nature, they are made perfect, so they are even mightier than those of us on earth.
“The prayer of the righteous is powerful and effective” (Jas 5:16). Are not those in heaven righteous & therefore their prayers powerful and effective?
Mary in particular is a mighty intercessor because of her special relationship with Jesus. We can see this from two examples, one from the Old Testament and one from the New Testament.
In 1 Samuel 2:19-20 Bathsheba the mother of King Solomon petitions him on behalf of Adonijah.
So Bathsheba went to King Solomon, to speak to him on behalf of Adonijah. The king rose to meet her, and bowed down to her; then he sat on his throne, and had a throne brought for the king’s mother, and she sat on his right. Then she said, “I have one small request to make of you; do not refuse me.” And the king said to her, “Make your request, my mother; for I will not refuse you.”
Solomon was open to granting her petition, although it did not end well because she asked for the wrong thing.
Mary is our King's mother and we believe equally open to hearing her petitions on our behalf. Of course we can approach the king directly, but perhaps those (Mary & Saints) in the very presence of God can make our requests more eloquently than we can. And it must please our King that we honour and value his mother just as he does.
Then consider the wedding at Cana in John’s gospel. They are short of wine; Mary sees the need and tells the servants “Do whatever he tells you” (Jn 2:5), and he responds. Mary was made aware of the need for wine. She then interceded on their behalf with her Son, who evidently was not going to respond to their need without her intercession. But because of her intercession, he then did respond.