my guess is that the stock rear springs are far too soft for the pathfinder even when new.
I bought the moog springs (advertised as oem replacement) thinking the original springs were sagging on my 2003, and it was the same thing, bottomed out whenever there was 4 people + luggage in the car.
I have also noticed that almost every r50 I see on the road sags a little or a lot on the rear
in the end I bought the ARB 2922 Old Man Emu Coil Spring, and KYB gas a just shocks, and my pathfinder rides a lot better, no more bottoming out and no noticeable change in ride comfort.
just changing shocks won't fix your problem, the job of the shock is not to carry the load of the car, using spacers will only level the car when loaded, but the spring will still bottom out.