I'd join, but wrong cities. I'd probably do it for the same reason you're considering it...just to experience it. It's your money. Do it, no matter the reason....If you want to use NK to go to an airport you've never been to, then GO FOR IT! If you want to use NK because you want to see just how bad they are, GO FOR IT!
If you never fly them again, at least when you trash them, you can say that you have been on one of their flights.
What could possibly be worse than not getting an upgrade? uhm....cancer, poverty, an STD...(do I need to add more?)