There is no compelling science case for Arecibo that can't be pursued with other telescopes, especially since the frontier of radio astronomy has mostly moved from sensitivity (requiring big apertures) to resolution (requiring long-baseline arrays), or to shorter mm/submm wavelengths that Arecibo can't handle.
Sorry, but that is not true. Radio astronomy needs improvement in a wide variety of areas in order to tackle the tremendously wide variety of science that is done at radio bands. Examples include sensitivity, field-of-view, dynamic range, image fidelity, resolution, and wavelength coverage. But sensitivity is one of the most important. That is why the SKA is on the table to be the world's next generation decameter/centimeter wave radio telescope. The most important thing it provides is sensitivity (i.e. SK = square km = sensitivity). And Arecibo is already a 5-10% SKA.
For my own research (pulsars), Arecibo's sensitivity is what sets it apart. Although, truthfully, the fact that it can't observe any of the southern sky (where most of the pulsars are) is a definite downside.
Finally, you mention surveys and imply that because Arecibo is doing a larger percent of them now that that means it is washed up. However, that also isn't true. Modern astronomy is driven by large surveys (including several of the instruments that you mention, for example, Sloan, PANSTARRS, LSST) as they dramatically increase our discovery space.
I guess they didn't look at redundancy or reliability in their cost equation...So we marched down the road of the Windows platform. We don't have any Unix; we don't have an AS/400; we don't have any mainframes — we don't have anything outside of Windows. There has been tremendous cost savings....everything's Windows. Every technician that works on a server works on a Windows server. Every technician working on a desktop works on a Windows desktop. That's quite a bit easier than other flavors of desktops or OS/2 or whatever else is out there.
Those who can, do; those who can't, write. Those who can't write work for the Bell Labs Record.