For DX, same wideness can also be attained by getting lenses appropriate for that field of view. And dx lenses are cheaper to boot, not to mention the selection for dx lenses is actually wider.
For macro, dx is more useful due to the crop factor. It gives the impression of more magnification on the same focal lengths and working distance. As for high iso performance, most macro shooters will stop down for maximum dof and many will use artificial lighting.
Fx will be advantageous in low light shooting, recoverable dynamic range as well as thinner dof for same lenses with the same field of view.
1) pricing aside, my point is still valid right? comparing same focus length on FX and DX, FX will always be wider.
2) when using a small aperture and not-too-slow shutter speed (in case of movement of insect or wind), good ISO performance is still a plus especially when flash may not be applicable or an option.
just trying to clarify if my points given are entirely incorrect or are you just adding on to them?