Got the work done today: dealer replaced the CVT, the clutch, and the belt -- all covered under warranty. They said they now believe the initial problem (from day one) was a bad clutch, and that led to worn rollers, pulley, and belt.
While they couldn't say why the clutch was bad, they thought it was interesting that Kymco no longer provides the clutch that has been specified from 2010 on (and continues to be today). The replacement part is apparently slightly different and has a different part number. So the mechanic wondered if my problem might have been related to a previously known clutch issue.
Anyway, I haven't ridden it much yet, but was pleased to find it a lot smoother, while easily maintaining 60 mph. Hopefully the mpg will improve as well. The pickup has suffered a bit, but I'm not complaining, since its peppiness had always been amphetamine-like -- lots of noise and vibration. I guess all that engine torque is now spread out the way it's supposed to be. Feels great to have the sense that there's plenty of power in reserve. Looking forward to tomorrow morning's commute!