They've always seemed terrible to me for speed and thermodynamics reasons (it's so much easier and faster to move an electron than a bunch of neutrons). I suppose from a computational perspective you could do a simple, or set of simple computations in a machine more resistant to, or at least more resilient against, EMP (as the thing that is easy to move in a B field, that electron I mentioned above) is easier to move in undesired wave when subject to a large external B field. I doubt it though.

However you do raise the possibility of longer-lasting computers in other harsh environments, specifically space. The Voyager probes work in part because the feature size of the components is huge (discrete transistors that are inspectable through a microscope and in some cases the naked eye). Such components are hard to come by these days. Micro mechanical devices might even be a superior approach. And for most space applications speed is not critical.