Regarding your question on the Titanium Spark Plugs, it is a good idea to replace your standard plugs with THE CORRECT EQUIVALENT Titanium or Platinum or even better if you can. When Subaru introduced their twin cam 16 valve engine they marketed the vehicles so fitted with these plugs because of their longevity. It is not easy to change plugs on a 16 valver boxer engine, so the plugs are supposed to last 100,000 km. I would say it is expensive, comparatively speaking, but worth it.