But Marks, this does not account then for why he would say those things to the Laodiceans. They were Christians, yes? If they had Christ and therefore had all they needed, why was He speaking to them and about them using such spiritually impoverished terms?

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This here is key.
This is a great example that doctrines don't exist in a vacuum, and how you understand soteriology will affect how you may look at this letter.
This is also a good "litmus test" to the reader, in fact, Jesus does not say this to the members of the church in Laodicea, Jesus actually said this first to the messenger to the church. This was specifically who Jesus was speaking too, though of course all are invited to hear and benefit.
So there's the first question . . . was Jesus indicting an entire congregation of born again children of God? Was Jesus indicting the messenger specifically?
Revelation 3:14-22
14) And unto the angel of the church of the Laodiceans write; These things saith the Amen, the faithful and true witness, the beginning of the creation of God;
15) I know thy works, that thou art neither cold nor hot: I would thou wert cold or hot.
16) So then because thou art lukewarm, and neither cold nor hot, I will spue thee out of my mouth.
17) Because thou sayest, I am rich, and increased with goods, and have need of nothing; and knowest not that thou art wretched, and miserable, and poor, and blind, and naked:
18) I counsel thee to buy of me gold tried in the fire, that thou mayest be rich; and white raiment, that thou mayest be clothed, and that the shame of thy nakedness do not appear; and anoint thine eyes with eyesalve, that thou mayest see.
19) As many as I love, I rebuke and chasten: be zealous therefore, and repent.
20) Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me.
21) To him that overcometh will I grant to sit with me in my throne, even as I also overcame, and am set down with my Father in his throne.
22) He that hath an ear, let him hear what the Spirit saith unto the churches.
These pronouns, thy works, thou art, spue thee, all of these pronouns are singular. So this certainly descriptive of this messenger. Which is why I don't think "angel" to be the best translation in this case, though this is the simplicity of the KJV translation I've come to appreciate so much.
If you see this letter as describing a born again Christian being threatened with spewing out, and that spewing being the loss of eternal life, this shows not only different ideas about this letter, but also about salvation, rebirth, sanctification, it goes on.
In fact, these pronouns ARE singular, so how far down that road should we go?
Correct, in keeping with the latter rain analogy. It rains early in the season, stops, and then rains again, more heavily at the end of the season before the harvest comes.
In this then, you are thinking is that we've received the Holy Spirit as they did, yes, but now with the same power as they did? And one day this will change?
So even if I had faith to move mountains, God's answer would be, Nope, ain't happening! ?
Ephesians 1:3 Blessed be the God and Father of our Lord Jesus Christ,
who hath blessed us with all spiritual blessings in heavenly places in Christ:
This say to me otherwise.
Much love!