Lifting a 4WD is ok
Lifting a 2WD is ok
Lowering a 2WD is ok..
but lowering a 4WD is just the dumbest thing around.

You end up with a very slow, very heavy truck that handles only marginally better, and gets stuck off-road.

Without a bunch of money, you can't even lower an Xterra. You can't cut the springs because they're torsion bars. You can't just soften the front because it will ride on the bumpstops, lose all upward travel and handle like shit.

It's your truck though, so do what you want, but you have to realize that you are alone wanting to do something like lowering a 4WD vehicle, and you will get a lot of negative feedback because the idea is just plain stupid and serves no purpose.