There's not a lot of info on adding spacers on a Nissan Xterra- well besides don't do it.
As long as quality spacers are locked down though, the added exterior angle stress added on IFS suspension components is no more than using a smaller "correctly" backspaced wheel.
My X is sporting the supercharger package rims. Even with 3 inches of suspension lift and a 2 inch body lift, 285/70/17 (33x11.50) is the tire size I'm stuck with unless I keep it on road. I had always wanted the tires to be pushed out a hair to increase the looks and stance. When I got the new BFG KM2's, I went ahead and threw on a set of spacers from RuggedRocksOffroad.com as well. I ordered the 1" but they were out so I tried the 1.25" and they ended up working out just fine. For safety's sake, I used red loctite since I didn't plan on taking them off anytime soon. The threading happened to be different on the spacer studs compared to the wheel studs, so I had to use the lugs inside the spacer. Thought shiny, they still fit just right, allowing the spacer to sit flush and not enough room to work themselves out if the loctite should fail.
While the spacers looked fat before putting the wheel back on, after everything was buttoned up, the subtle look was just enough to look proportionally correct on the X. The most important part was that the wheels still stuffed just fine without any fender damage.
Stuffed side room