Shaw definitely intended an unspoken attraction between Higgins and Eliza--he just didn't intend it to be resolved the way it is in the musical.
The MY FAIR LADY movie is far from a "masterpiece". It's stiff, stagy, and too long. Audrey Hepburn is fine post-transformation, but her Cockney impression is very bad, and the inappropriately polished Marni Nixon vocals are jarring in a way that they aren't in the WEST SIDE STORY and KING AND I movies.
As for PRIDE AND PREJUDICE, Emma Thompson is hardly the first writer to take her name off a project that had become an embarrassment to her. Robert Towne did the same thing on GREYSTOKE: THE LEGEND OF TARZAN, LORD OF THE APES, as did F. Scott Fitzgerald on a score of old-Hollywood movies (in which he was employed as a hack, basically.)
I ask in all honesty/What would life be?/Without a song and a dance, what are we?/So I say "Thank you for the music/For giving it to me."