The scene is every bit as wonderful today as the gravity free hotel in Inception. The gimmick never looks dated or obvious for a second. It improves and overshadows Astaire's dancing in a good way.
I love the four wall dance but I think saying it is every bit as wonderful as the two Inception scenes sells Inception short. The dance really works in this context, but you can always see the choreography hitting "testing" or transition points. It doesn't break the scene at all but compared to the incredible pace and fluidity of the Inception scene, I don't find it quite as memorable. Mostly I just want to say (not in response to anything you suggested) that the fact that the Inception scene isn't entirely novel in no way takes away its incredible effectiveness.
I too like the Astaire dance in the ship's gym. I'd watch a movie that was just Astaire moving room to room in a house, finding ways to incorporate the props and furniture of each setting into a dance. The third sequence that stands out to me was Liar All My Life, for its comedy. Three things that strong is enough to earn this a recommendation. Astaire is of course fantastic here and I find a lot to like in his half of the romantic double-header. I'm surprised 1SO didn't mention Sarah Churchill who plays Astaire's love interest, Anne, she having a reddish tone to her hair. She's a little stiffly British but solid. Powell is okay here when she's not singing but her songs lack the energy of Astaire's and don't fit with the rest of the tone. She has a few moments of the plot that work but generally it is unimpressive. The film knows where to put its biggest bet.