I also noticed a wobble after rotating the tires, and even more so when I installed wheel spacers. I checked the torque on the spacers and then the rims after 20 miles of driving and they're still properly torqued. I was told it was the wheels needing to be balanced. If it is the rack needing adjustment, how would I go about getting that tightened back up? I know it's not my ball joints or tie rod ends, as I have recently replaced those and had an alignment done after the install.
Get the tires balanced and go from there.
ALSO - are your spacers hub centric? If not - get some.