Don't add wheel spacers unless you need them. Yes...I suppose that they do give you a slight increase in stability in an off-camber situation - but that's such a small amount that you'd be hard pressed to notice it. To be honest, your rig will already handle an off-camber situation that would leave you pulling your driver's seat out from between yer cheeks
On the down side, wheel spacers do have three downsides:
#1. You need to own a torque wrench and use it to run spacers successfully - just ask Jackstand Johnny what happens when you don't torque things. Here's a hint...it's not good when your wheel gets to the next bend in the trail before your front bumper does.
#2. Your stock fenders will no longer cover your tires. I run spacers with stock JK flares, and the sides of my jeep are never, ever clean. The buildup of slush thrown by my front tires onto my rear fender flares can be inches thick during the winter months.
#3. Spacers will shorten the life of your unit bearings. The JK unit bearings are already somewhat short-lived. Why cause yourself more work?
Don't think that I'm running down spacers in general. I've run mine happily for the past two years. If you buy good quality spacers (like Northridge sells), install them properly with loc-tite and a torque wrench, and maintain them, you'll be fine...but why spend the money up front (and the extra money and time for maintenance and changing unit bearings) if you aren't going to see any real benefits?