The similiarities begin, first, with the humor. Dodsworth is a serious film about a truly horrible wife who gets more and more horrible as the film continues (and yet manages, through a well-written script, excellent acting and great directing to avoid becoming villanious; her horribleness is the real horribleness of real people, not the cliched horribleness of film) but even Dodsworth is threaded through with darting amusement, and The Good Fairy is pure, lovely comedy. It is possibly the funniest film I've ever seen, and I highly recommend it (I highly recommend both, but I had a hard time enjoying Dodsworth, I hated the wife so much). As with Billy Wilder, the comedy of The Good Fairy gets better and better as it continues from the great line (from the waiter to the heroine about a plate of hor d'oevures), "Here, have some leftovers" to the Lothario's line, "When I'm full of Dutch courage, I behave very Frenchly," not to mention the pencil sharpener and the "Foxine."
The other Billy Wilder similarity is the underlying current of bittersweet pathos. When, in The Good Fairy, Herbert Marshall rushes to stop Margaret Sullivan, he reaches her and slumps against the door. In that one movement, the romantic rush becomes more human, almost forlorn, and touchingly uncertain. It's a Billy Wilder touch (although presumably now, it's also a William Wyler touch).
I do think that William Wyler is more of a romantic than Billy Wilder. With Billy Wilder, one is never sure of his perspective. He distances himself from his lovers; subsequently, the underlying pathos can veer towards cynicism (where it just skirts the edge). Wyler, on the other hand, cares deeply whether or not his lovers find resolution. I was invested in both his films. (You know a movie has you when you start yelling, "Oh, just leave her already" at the screen.)
Now, I'm not one to believe that older films are automatically better (You've Got Mail is high on my list of excellent modern comedies) but it's hard to imagine The Good Fairy being reworked. The thing that makes it so fine is that it winds a cliff-edged path between broad comedy, sexual innuendo and human drama, all accompanied by perfect dialog. However, in this current day and age of snappy scripts (Gilmore Girls, House, MD, Joss Whedon), perhaps the days are coming when that subtle but difficult path could be tread again. In the meantime, who needs the color version when you've got the black & white?