I assume for flying N-reg you hold a standalone FAA PPL and not a 61.75 validation based on the Part.FCL license (in which case your flying would have been illegal).
You assume correctly; it's actually the other way around in my case. The German-then-EASA licenses came from the FAA certificates when I was stationed here a few years ago. I've not done much power flying in Europe.
I don't particularly care if I renew the SEP or not. I can fly N-reg via the base flying club cheaper. However, if it were reasonably priced and convenient then I would do it. It's not worth several hundred Euro just to save three hours in the motor glider.
It has been more than three- and less than 12 months, so supposedly I "should get an assessment, two hours of dual, and a check flight." This weekend I flew 2.4 hours including six landings, an ILS approach (with safety pilot), and had a PPR for the largest USAF base in Germany. I don't need "training," I'd just like to fly with an examiner. Doesn't seem possible.
If I could find a place to do some aerobatic training and combine it with a renewal then it might be worth it!