Archer,
What do you think? Other than finishing off that FAA IR what would any further American ratings do for you? You've got what you safely need for the US touring and you're not wasting too much time or money on ratings that are useless in Europe.
Some will be divided on the worth of the FAA instrument ticket and its usability back in Europe. I favour finishing it. Great experience, builds on your skills, hopefully further develops judgement over time and exposure to the IFR system and could just save your life.
Regards from the Towers
Rob