I'm not sure his wheels are currently without issue. Sounds like he was feeling like the wheels were not performing well with a very small load. If that's the case, it might still be worthwhile to upgrade at least the rear wheel to whatever the maximum spoke count can be found.

But even then a trailer would be worth considering. I have done trips with panniers and trips with trailers. They both have their pluses and minuses, but definitely one of the huge upsides of a trailer was that the bike had none of the weight, and felt almost the same as unloaded, especially when the way ahead was straight and flat.

I have no experience with the Extrawheel or any single-wheel trailer, but it always looks to me like they might be more difficult to balance the load so that most of the weight was supported by the trailer wheel. Maybe that's not the case, but I want to throw it out there, because the OP's goal is not more gear capacity, but rather less stress on the rear wheel. To my mind, not backed up by experience, a two-wheeled trailer would be better for that.