I agree with your comments for the most part, and perhaps I do need to provide clarification regarding "spiritual death" and "died".I saw your request for definitions. That's so important, imo.
Your passage says the "mind" set on flesh or the "mind" set on Spirit. Isn't one's "mind" the same as one's "spirit"? I think it is. So in essence, your passage can be read "for the spirit set on the flesh is death, but the spirit set on the Spirit is life and peace".
In either case, the spirit of the man is active, and activity is not indicative of a state of "spiritual death"--unless we redefine "death" to mean "active in a way that is displeasing to God" or some such.
This is my problem with the spiritual death concept--it depends on redefining "death" to mean something other than what we normally recognize as death, similar to what you posted here:
This makes plenty of sense to me, and if you are correct, when did it change?
You followed with this "Spiritual death is a state (those who have not been born of the Spirit lack Spiritual life). But there is no such a thing as dying spiritually", which I find interesting. Once again, our normal idea of "death" is not a "lack of life" but a "loss of life". Is there anything that is ever dead that wasn't ever alive? Babies that are "born dead" (or stillborn, another indication of death meaning inactivity) were at one time alive in the womb.
So if Adam ended his life in a spiritually dead state, surely he "died spiritually", right?
And if a man is not condemned for the sins of his father ([Eze 18:20 KJV] The soul that sinneth, it shall die. The son shall not bear the iniquity of the father...), and "all have sinned and come short of the glory of God", then it seems the problem is not "spiritual death" but a proclivity (nature?) to sin that brings on the penalty of death. Though the death appears to be a foregone conclusion even before sin after Adam. (Rom 5:14)
I was at one time "spiritually dead" (by my definition) and in need of being reborn. This does not mean that I "died spiritually". What I think was Christ's meaning regarding the "dead" (like "let the dead bury the dead) is simply that these are people who have not been born of the spirit. Were we talking about physical life and someone introduced the idea of a rock being alive we could correctly say that a rock is dead (not that the rock died but that the rock lacked physical life).
I believe that when we go to far we end up missing the point. Adam was not (I think obvious via Scripture) spiritually alive and then died spiritually. But again, it does go to definitions.