I also had this issue (to a lesser extent), and found that some oil was leaking into one spark plug well (but not very much), so I replaced the entire valve cover on that side. While doing some research, a 350Z enthusiast was having oil consumption issues and discovered that narrow channels in the passenger side valve cover can gum up and cause the PCV valve to allow abnormal amounts of oil back into the intake manifold, and thus burned right out the tailpipe.
I would certainly recommend the $200 for a new valve cover to rule this out, as the other causes are far more expensive to repair.