Funny enough, this concept is explored in The Motion Picture novelisation by Gene Roddenberry.
It is very, very rare for Vulcans to have a mind link, or bond, with another individual that can be achieved without some form of physical contact -- thought to be unheard of between a Vulcan and a human.
That is what a lot of Vulcans aspire to achieve in their relationships and connections. Roddenberry coined that as a*T'hy'la* bond in Vulcan culture.
Spock is basically outed as having that type of bond with Jim Kirk in TMP novel when he is attempting to complete Kolinhar. He fails it because when the Vulcan elder melds with Spock's mind, she can actually hear Jim Kirk's worried ruminations in Spock's mind -- on Vulcan -- all the way from Earth.
Anyway, that is particularly scandalous, and largely unheard of, in Vulcan culture. The elder instructs Spock to take leave of Vulcan and answer this call, as "his place is elsewhere".
This post summarizes that moment in the film beautifully while conveying more of the emotion of TMP novel -- that it was the connection to Jim that Spock could not sever or let go of in order to complete Kolinahr.
Shout out to @kristascoffee-blog1 for creating these gorgeous gifs and the OP which articulates this moment so well.
In the movie version, Spock's summoning is depicted as solely being about sensing V'Ger.
In the novel, it is because he is essentially caught having a T'hy'la bond with Jim Kirk that is strong enough for them to hear each other *on other planets*.
In TMP novel, Roddenberry describes Spock and Jim's mind link as a very unique, rare and much sought after type of bond that is revered in Vulcan culture.
Roddenberry wrote: "For Spock, theirs had been the touching of two minds which the old poets of Spock's home planet had proclaimed as superior even to the wild physical love which affected Vulcans every seventh year during pon farr." I mean . . . That's pretty major. LOL
I thought they were intentionally nodding to that quote about poets and the T'hy'la bond from the novel when Pelia referred to Kirk and Spock's connection as "poetic", a reference to how Spock himself thinks of their bond in TMP novel.
I always felt the film version lacked a great deal of that incredible humanity and affection found in the novel because they were so late getting Nimoy involved. They didn't have enough time filming with him to deeply explore some of the more meaningful moments with Spock on screen outside of what we did get.
In the novel you get to hear all of his pained, desperate, and insecure thoughts. How much his heart is bursting when he first comes aboard the Enterprise. But we see little of that inner turmoil displayed in the film, sadly.
I know given the opportunity and time, Nimoy would have done a wonderful job with fleshing out Spock's story, because honestly, TMP is about Spock. V'Ger simply mirrors what he is going through and helps him realize where he belongs.
They just took so long getting Nimoy involved, they barely had time to film with him. So the story feels very cold on screen, and that's too bad, because the book actually made me weep when I read it growing up because it moved me so much. It has so much heart, and it is at its core a beautiful story of self acceptance -- a willingness to be vulnerable and accept love.
Spock starts the book like V'Ger -- cold, broken, and desperately seeking answers to the meaning of his existence.
He attempts Kolinahr and is refused by Vulcan when they realize he has a T'hy'la bond. They tell him to seek out the voice calling him, as that is where he belongs.
He comes full circle in the sickbay scene when he takes Jim's hand and admits that V'Ger is what he had aspired to, and he doesn't like what he sees -- he realizes the incredible value in the simplicity of love, trust, and loyalty.
TMP is actually supposed to be about Spock and how his journey from shame about his connection to Jim to unabashed pride mirrors V'Ger's experience.
V'Ger also goes from being cold and barren to discovering the potential and value of human love. Sadly, they took so long to get Nimoy signed on for TMP that the end result was a story that really wasn't about Spock or his journey, even though the novel almost entirely focuses on what Spock and Jim went through and how that parallels V'Ger.
Spock tries Kolinahr, Jim tries admiralty, and they both end up miserable pursuing what they *think* the next step naturally should be, not what they actually want. The conclusion is them actually accepting that they are far, far better together than they are separate.
Their T'hy'la bond, this form of Vulcan bonding thought to be so rare it is often considered a myth on their planet it is considered so unattainable -- this bond is shared between a human and half-human Vulcan.
It solidifies that Vulcans actually stifle themselves and their potential when they get too hung up on being pragmatic, stop at logic, and don't explore beyond logic as a meaning to life. As Spock says many years later, logic is only the beginning of that exploration, not the end. Spock has grown by not permitting himself to have such limitations.
So in summary, you are absolutely right -- this kind of mental bond or connection is extremely rare in Vulcan culture, and seldom seen without there being a physical connection to establish a link.
The absolute irony is, a rare Vulcan T'hy'la bond is shared between a human and half-human Vulcan, while many full Vulcans will live out their long lifetimes without ever knowing what that is like.
