Second pilot?
I believe that in an inadvertent IMC situation, a second pilot may only confuse the first pilot and vice versa. At best, maybe encourage the PIC to abort the mission sooner. I would rather have a non-vertigo prone autopilot. One whose default position is wings straight and level. One that is easily overridden in order to climb, communicate and confess. One that will resume straight and level if the pilot gets confused. Most pilots that lose it in IMC do fine in their bi-annual instrument check ride. It's the emotional fear element that trips up the pilot in a life-threatening unfamiliar environment. It's called sensory overload. An autopilot is like that check airman when you are under the hood. You almost never need them, but it's calming to know that they're there.