Foxmulder, interesting idea. After thinking about it for a while, I would agree, but I have found other lines than you.
My proposals for the TOS-based films (as the others are not so present in my mind) with a short explanation for each of my choices. I have found that in most cases, a special line of dialogue is used like a kind of front and end book covers to the films.
TMP: "He wanted her back. He got her!"
Spoken by Sulu, refering to Kirk and the Enterprise. Of course, we fans wanted the Enterprise and her crew back on the screen and that was the reason for the success of the film, rather than story and execution. If Kirk sends her "Out there. Thataway!", we will watch, no matter what heading or purpose (or lack thereof).
TWOK: "How we deal with death is at least as important as how we deal with life, wouldn't you say?"
Spoken by Kirk to Saavik. The whole film circles around the topic of aging, loss and death and this line is especially set up in the beginning of the film to be repeated (by David) in the end.
TSFS: "Because the needs of the one ...outweigh the needs of the many."
Spoken by Kirk to Spock. This has to be the characterizing line of not only this film but the trilogy of which it forms the central part. It was set up (in reverse) by Spock at the end of TWOK and quoted again (by Amanda) at the beginning of TVH.
TVH: "I want you all to be very careful. This is terra incognita. Many of their customs will doubtless take us by surprise. [...] This is an extremely primitive and paranoid culture."
Spoken by Kirk, these lines about their ancestors (us!) sums up the basic concept of the film nicely.
The B-story of Spock, getting over 'not exactly working on all thrusters' of course is nicely depicted by the lines "How do you feel? - I do not understand the question. The question is irrelevant." and "Tell her ...I feel fine."
TFF: "It's a mystery what draws us together. [...] Other people have families. - Other people, Bones. Not us."
Spoken by McCoy with a response from Kirk. It was one of Bill Shatner's expressed goals to show-off the Enterprise "family" of comrades in his film - and in that area he had the most success. Again, this line is referred to at the conclusion of the film.
TUC: "Only Nixon could go to China."
Spoken by Spock to convince Kirk to make peace with the Klingons. It was made clear at the time of production, that this film is meant to be a comment on the end of the cold war. The producers avoided (cleverly) mentioning this fact directly, rather reminding the audience of a (somewhat) similar phase of warming relations two decades earlier.
Btw, the "book covers" in this film is the talk about the Enterprise and crew about to stand down.