I installed the KORE Leveling kit on my '06 at about 1K miles. It is a quality kit, good instructions, took about 4 hours to install.
My truck is level. I also installed the Billstein shocks in the rear at the same time, wanted them to be the same as the front. The kit and the added rear shocks made a world of difference over the stock shocks. Nice ride, I would certainly do this kit again. I have a little over 30K on the KORE kit and have had NO problems with it's components or any front end issues. My tire wear is the same side to side, measured it with a tread gauge.
I agree that the spacers DO seem to give a rougher ride, I used them on another truck and ended up taking them off. I live on a long, washboard road, it was unbearable with the stock springs/shocks, I had to travel at a creep about 15 mph it was so bad. Now, I travel at 35-40 mph.
I considered install ing the mini packs, also considered the full leaf replacements, installed air bags instead. I also installed the KORE single steering shock. It has made a world of difference in the slight RH pull due to road taper.
CD