They make a Z400 with similar styling that's much cheaper.
While nothing (mainly) wrong with the Z650, I'd spend the extra and get the Honda 650 for the sweeter sounds of the I4. And I prefer the styling too (but understand why some would prefer the Kawi styling).
If you're now considering parallel twins, the Yamaha MT-07 sounds far better and is well loved by owners. Cheap, too.
If a Z400 can be had for much cheaper than a Z650, that's where I'd go. The 650 is okayyyy-ish, but not as exhilarating as its styling would suggest. The 400 is so light and compact, it's just a hoot to throw around, yet still with enough power to be fun -- especially while learning.
I'm not a fan of the CB650R -- waaaay too much money and really not that fun to ride, either. It's smooth and looks pretty good, but seems lacking in character to me.
Z900 is a LOT of engine. You're making me miss mine. Turbine-smooth and sizzling power. It would be a far more hooligan-friendly machine than an MT07, that's for sure.
What about the looks of a XSR700 instead? Proven drivetrain. Better styling. Should be enough of them around to find a bargain?
And also... Jaeger, I might have an insurance solution for you. PM sent.