I think the problem w. 15 Broad is that construction delays have allowed wy too much time for buyer's remorse to set in and fester -- as other, newer developments pop up (20 Pine anyone?), they decide to add units, thus diluting the "exclusive" atmosphere, and people ask themselves, "How much do I really like bowling, anyway?"
That said, new contracts are still being signed there, so all is not lost! Does proximity to the new Claremont Academy help?
The club residences at Cipriani are another breed entirely -- you pick a certain unit, fully furnished -- if you want unit 20B, for example, you've got to take the furniture that comes with it -- no swapping, so it's kind of like buying a hotel room. This is definitiely for the pied-a-terre crowd, not people who'd actually live there full-time.
An odd place for a pied-a-terre perhaps, but it depends on your reasons for being in Manhattan, and I guess the amentities make up for the perhaps unusual location.