Watch the film again, Tucker's story almost resembles Coppola's and his film career. There are many paralells for both men. Just take away the cars and make it film. Tucker is Coppola. So it's not just the cars, Coppola loves him because he was able to stand up to the big men like Coppola, and had to fight hard for his independance. The story of the seat belts being a closed discussion is very similar to the story of a Paramount exec telling Coppola that the discussion is closed about Brando on The Godfather.
Coppola had wanted to bring Tucker's story to the screen for along, long time. His interest began when Coppola's Dad had ordered a car, whcih never came, but it fired young Francis' imagintation. As time went by, Coppola read up on Tucker and came to identify with him and his maverick ways. That is declared by Coppola in many books and interviews. "This won't be the first time we worked for nothing!" is a line read by Frederic Forrest as Eddie in the movie. He ought to know, as he went with out pay when Coppola could not meet the payroll on "One from the Heart". The scene where Tucker throws the telephone against the door and breaks it echoes the frustration he felt and expressed during the making of "Apocolypse Now" and he picked up his Oscars won for "The Godfather" movies and threw then out the window. His children recovered the broken statues. In the movie Tucker's daughter picks up the broken phone.
Coppola was also derided for his revoluntionary movie techniques known as the "Electronic Cinema". "The Kid" in Tucker played by Elias Koteas near the end of the movie grows a beard on Tucker's advice like Francis told George Lucas to do. Everyone called George "The Kid" before the beard.
The former aircraft plant also speaks of the Hollywood General Studios that became Zoetrope Studios where Francis could make every movie he wanted. That dream also came to an end after "One from the Heart" (a landmark movie --not without its problems).
Tucker's son, played by Christian Slater, also represented Coppola's son, who in real life seemed to be the one that would follow his father's footsteps in filmmaking before his tragic death during the making of "Gardens of Stone". The film "Tucker: The Man and his Dream" is dedicated to him ("For Gio, who loved cars"). Of course, Sophia rose to that position.
Lots of other details. It is definately a very personal film and a very wonderful one at that.