I think it's claim to fame is it's unique. I don't know of any other film that has done this - not for an entire movie anyway.
Your analysis is valid, but even though the film lacks cohesion, it's still kind of brilliant considering it is a patchwork of other material.
I agree with your idea that creating a plot and telling a gripping story while paying attention to continuity was probably not the priority, but secondary to the gag of splicing in old films and making up jokes around that device.
It's kind of neat seeing so many big names (from a bygone era) altogether in one film when such a feat would have only been a fantasy for an actual movie of the time.
It's not as funny as a lot of other Steve Martin's films and a lot of the humor relies on the gag of mixing new footage & dialogue with existing footage, but it still has it's moments... even some that don't rely completely on it's distinctive gag (such as the "
Pajamas!")
For years I've been referring this movie to @
Citizen Rules, only because he is a Noir buff and this is the only Noir spoof I know of that utilized real clips and stars from real Noir movies to create such a comic fiasco.