Re 2, for human imaging, the noise from the body is far greater than the noise in the receive coil, so there's no real benefit. In high resolution NMR of small samples, however, the noise in the detector coil & preamplifier chain dominate sample noise, so there is a big benefit to using a supercon. receive coil. But. (There's always a "but.") Even then, one must determine the practical consequences of having a high quality factor coil. There are reciprocal effects of coupling a large signal to a high sensitivity coil; phenomena such as "radiation damping." It means that supercon. coils are only really beneficial under certain situations, they aren't universally better than room temp copper coils.