ChainsawAsh said:

However, the 1973 cut should still be preserved for historical reasons. The fact that the 1973 cut of American Graffiti and the 1971 cut of THX 1138 have never been released on home video in any format is even worse than Star Wars' situation.

I imagine the THX 1138 cause is much more lost than Star Wars. However, considering some of the skill on this very board, getting a high quality 1973 theatrical version of American Graffiti is probably fairly easy. Cut out the three 1978 scenes, edit back in the original title card, switch the sound to mono. I don't know the quality of the title card shot from the documentary, but it may be the same as the film.

The three scenes cut in 73, then added back in 78 are;

Toad and the used car salesman - "Say, that's a really beautiful car you have there."

Steve telling off one of his former teachers - "Why don't you go kiss a duck."

Falfa singing Some Enchanted Evening.