There's a slight problem with simply deeming Plan 9 "better" and Unix (for whatever value of Unix-ness) "good". Depending on your definition of worth, it's probably easy enough to find a system that is even better, i.e. more "pure" in that regard. Obvious examples, if your focus is underlying concepts, would be Oberon and Lisp Machines, where it's straight access to data structures and functions, without superfluous parsing of lines of text and command line arguments...
Compared to really other systems, Plan 9 is still Unix. Don't think the designers would disagree...
Plan 9 is Unix in the way that Unix is still Multics. So is Plan 9 still Multics?
Really, the superficial similarities should not overshadow the fundamental differences. QnX is also Unix by that definition, but in fact is a completely different system under the hood.
Compared to the others I've mentioned? Sure, and that would most likely mean that most systems are closer to Unix than e.g. SmallTalk. Probably even including Windows, unless one would have a very favorable view of COM.
Compared to really other systems, Plan 9 is still Unix. Don't think the designers would disagree...