Well, I'm on my 4th C650GT in as many years. I crashed my original 2013 after 6 months on the 101 in central California with 12K miles on it. Got a replacement and put 55K miles on that in the following few years, until I traded it in in 2017 for a new C650GT (it was a 2016 model; the dealer told me BMW didn't import any 2017 models). One year later (to the week!) my girlfriend rear ended me as we were riding to Tombstone - had 17K miles on it by that point but sadly it got totaled. So I replaced it on May 12th with a 2018 nodel, and have just turned 10K miles on it.
I like to ride!
Meanwhile, one thing I find interesting is the improvement in MPG on the 2018 - while it's a touch slower off the line and can only get up to about 103MPH tops (the others could hit 110MPH) this new one gets far better mileage - around 60MPG if I keep it below 65MPH, compared to the 48-50MPG I got on the earlier models. BMW must have done something like detune the engine a little bit for better mileage at the expense of top speed.
Nice and good observation.