I guess you need to find 999999 more folks that haven't, because I have.
We had sold our 250, have had many other bikes in the garage, yet I picked up a new one last year because I really missed having a ninjette.
If the question is if someone would go back to a ninjette as their only motorcycle after they've spent a bunch of time on other bikes as well, perhaps that may be less likely, but it's certainly not unheard of. But that's not due to the cc's, it's because there may be bikes out there that may be better suited to one's particular interests. No one bike is perfect for everything, even our beloved ninjette.