I think it comes down to why you want one. As others have said, great motors and possibly less-than-great handling. For me, a Z1 would bring back the memories. That's why I have two 70s bike now. But (insight coming), when I get back on one of my 21st century bikes, I'm blown away by how well they do everything.
Sure, I would buy a Z1 in a heartbeat if the right deal came along, but I would probably get pretty much the same fix with the new Honda CB1100, and it would have 21st century technology.
Bob