“…the lines sound theatrical. In particular the character of Lydecker boasts a language that you would now only hear on the stage.” Though don’t you think Aaron Sorkin gets away this style of dialogue?

Laura is a fantastic film. Who wouldn’t fall in love with Gene Tierney?

I think the “alternate dream ending” story might be apocryphal. There is a deleted scene where Laura tells the detective that Lydecker imagined his first meeting with her.

Another film noir, also released in 1944, does have a “dream” ending – The Woman in the Window by Fritz Lang.
Edward G. Robinson wakes up at the end of the film relieved to discover his ordeal was, yes, all a dream!