Well, you must admit that they have a little bias: they can all read C++ fluently. Such a documentation would be useful precisely for those who can't.
I read C++ fluently (and have been doing hardcore C++ development since the mid 90's) and although I do agree that "what we have is a spec written in C++" I do not think we really want this to be the case in the future (even C++ itself has a "spec" - ISO/IEC 14882:2003 currently).
Transitioning from "C with Classes" to C++ took many years and it took many more for vendors to get "up to spec" (Microsoft being one of the main lagers until Herb Sutter joined them).
The same "slow" process will need to take place with Bitcoin as I don't think having "source code" as the "specification" (written in any programming language) is the correct (or desirable) way that things should be done (however I do appreciate that until the "source code" has any quirks that the don't make sense to put in the "specification" removed over time then the "specification" will also have to include them).
Algorithms are not described by "source code" and neither are any of the major internet protocols or programming languages (that aren't privately owned) - I can't see why Bitcoin *needs* to be an exception in the long term (although I do agree that in until a spec that matches the way the "reference client" behaves perfectly is written it cannot take precedence).
I guess the main thing I disagree with is that "it is useless/pointless to even try" (and BTW C++ had a "draft spec" for many years before finally becoming approved and adopted as being "standard").
This is not something that can or should be "rushed into" but something that like Bitcoin itself would need to evolve over time.