I confess I find the Scriptures adoption of the language of gnosticism annoying. ;-` But I'm glad that through it captives to that motif have been lead to their freedom.
The flesh vs. the spirit to the Greeks and mystics is a divide of the dimensions of man. But in the Lord's Word to us, it is just what you have said, a distinction between the fallen nature (in all its aspects eternally separated from God) and the new nature (in all its aspects eternally united with Him) and that because it is of the dimensions of God and man fully related!
I don't know the Greek word for "Spirit," used in the declaration, "the mind controlled by the Spirit is life and peace," but the Spirit is the Spirit of God Himself breathed into us by the precious gift of the lain flesh of Jesus the Unifier. And because of this new breath breathed by the willing, all that is of a person has come under it's power, by the authority of the Word it carries.
As I walked out of that cultic church a few years ago, one who was sort of "strongly suggested out" just before I left pointed me in the direction of a book by another man of might, Jesse Penn (mightier than the Body) Lewis. It was so wonderful to be reassured in his book, that God has given me a will -- and a will to be a will! -- a will which is all mine and not ever to be violated, nor dominated, nor dissipated, not by any creature and not even by God Himself. Why? For the very reason He made life: because He did not want to be succumbed to, but to be fully agreed with and very, very, very wilfully embraced. Ho, the difference!
That is a good test of whether one is free from gnostic notions: whether one is confident in God's gift of full person and an autonomous identity in all aspects of our lives, an identity in which we may run to willingly unite with His, yet as two individuals, and yet still in a unity which is utterly autonomous as a new joined relational identity, after the God-Man Himself. We never cease to be any less self in this relationship. However, we find self's other! We find a new fathomless giving of each other, God to me and me to God, a giving past death, that is a new living phenomena in all of creation, not possible had it not been for both the fall of the first Adam and the rise of the Second!
Thus, my reason is free, my emotions are free, my head and heart are free, and my will is enabled to agree with God in winning the soul's ground for the dwelling of one God and me.
Die, to live, yes, in Christ. But done once and for all. And yes, we still have the fallen nature to drag along with us until our earth bound bodies are worn down, but yes, it is not us anymore. It is as you say, just what was. And yes, we still have our old Adamically cursed bodies, but even they as degenerate as they are, are sanctified by what the vessel contains and until the new thoroughly pure flesh is put on.
Oh what we know! Oh WHO we KNOW! (when we are what we may be).
Yes, creation is expanding.
I have a real problem with willfulness. It was willfulness that caused Satan and Adam to fall, and it was for willfulness that Moses laid the book of the law as a testimony to the children of Israel.
And the serpent said unto the woman, Ye shall not surely die: For God doth know that in the day ye eat thereof, then your eyes shall be opened, and ye shall be as gods, knowing good and evil. And when the woman saw that the tree [was] good for food, and that it [was] pleasant to the eyes, and a tree to be desired to make [one] wise, she took of the fruit thereof, and did eat, and gave also unto her husband with her; and he did eat. Genesis 3:4-6
Take this book of the law, and put it in the side of the ark of the covenant of the LORD your God, that it may be there for a witness against thee. For I know thy rebellion, and thy stiff neck: behold, while I am yet alive with you this day, ye have been rebellious against the LORD; and how much more after my death? Deuteronomy 31:26-27
Saying, Father, if thou be willing, remove this cup from me: nevertheless not my will, but thine, be done. Luke 22:42
Who being the brightness of [his] glory, and the express image of his person, and upholding all things by the word of his power, when he had by himself purged our sins, sat down on the right hand of the Majesty on high; - Hebrews 1:2
Let this mind be in you, which was also in Christ Jesus: Who, being in the form of God, thought it not robbery to be equal with God: But made himself of no reputation, and took upon him the form of a servant, and was made in the likeness of men: And being found in fashion as a man, he humbled himself, and became obedient unto death, even the death of the cross. - Philippians 2:5-8
Neither pray I for these alone, but for them also which shall believe on me through their word; That they all may be one; as thou, Father, [art] in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me. John 17:20-21