As I understand it (as a lapsed IR(R) holder) spatial disorientation isn't caused by anything the instruments are telling you, it's caused by your inner ear giving you messages that don't tally with what's really happening.
As a result, your body is telling you (say) that you're banking to the left, when in fact you're flying straight and level. You compensate by banking right, which means you're no longer flying straight and level any more.
No amount of instrumentation will help with that. Automation might, but you need to be able to cope without any automation in case that fails.