However, I do think there is some merit in getting those in the actual field of functional and "good" design (as the author defines it) to weigh in on why precisely your design is just that. In my own UI/UX research, users all too often miss fully comprehending the painstaking research and work that goes into truly effective and good design.
I guess what my argument really is is that I would prefer to weigh more heavily the affirmation of those in the design field rather than a broad range of users with no particular ethos concerning design. Of course, who we end up designing for is the normal user, and what they think is indeed important. However, if 100 people said my design was good vs. hearing that from, say, Mike Matas, I would pick Mike Matas.
Your target is the users, if the users aren't having a good experience, you're not doing it right.
My experience with user testing is that if you give someone a UI and watch what they do with it (without instruction), you will quickly get a feel for how close to the mark your design is. Different users have different expectations of course, so you need to do this with a fair range of users.