Folks remember, VAX was not designed with UNIX in mind. It had two primary influences, assembly programmers (Cutler et al) and FORTRAN compiler writers. The truth is, the Vax was incredibly successful in both UNIX and its intended OS (VMS) sites, even if a number of the instructions it has were ignored by the C compiler writers. The fact the C did not map to it as well as it would for other architectures later is not surprising given the design constraints - C and UNIX were not part of the design. But it was good enough (actually pretty darned good for the time) and was very, very successful - I certainly stopped running a PDP11 when Vaxen were generally available. I would not stop doing that until the 68000 based workstations came along.
From my own experience, when Dave (Patterson) was writing the RISC papers in the early 1980s, a number of us ex-industry grad student types @ USB were taking his architecture course having just come off some very successful systems from the Vax, DG Eagle, Pr1me 750, etc.. [I'll leave the names of said parties off to protect the innocent]. But what I will say is that the four of used sit in the back of his calls and chuckle. We used to remind Dave that a lot of the choices that were made on those machines, we not for "CS" style reasons. IMO: Dave really did not "get it" -- all of those system designers did make architectural choices, but the drivers were the code base from the customer sites not how how well spell or grep worked. And those commercial systems generally did mapped well at what the designers considered and >>why<< those engineers considered what they did [years later a HBS professor Clay Christensen's book explained why].
I've said this in other forums, but I contend that when we used pure CS to design world's greatest pure computer architecture (Alpha) we ultimately failed in the market. The computer architecture was extremely successful and many of miss it. Hey, I now work for a company with one of the worst instruction sets/ISA from a Computer Science standpoint - INTEL*64 (C), and like the Vax, it's easy to throw darts at the architecture from a purity standpoint. Alpha was great, C and other languages map to it well, and the designers followed all of the CS knowledge at the time. But as a >>system<< it could not compete with the disruption caused by the 386 and later it's child, INTEL*64. And like Vaxen, INTEL*64 is ugly, but it continues to win because of the economics.
At Intel we look at very specific codes and how they map and the choices of what new things to add, how the system morphs are directly defined by what we see from customers and in the case of scientific codes, how well the FORTRAN compiler can exploit it -- because it is the same places (the national labs and very large end users like weather, automotive, oil/gas or life sciences) that have the same Fortran code that still need to run ;-) This is just want DEC did years ago with the VAX (and Alpha).
As an interesting footnote, the DNA from the old DEC Fortran compiler lives on "ifort" (and icc). Some of the same folks are still working on the code generator, although they are leaving us fairly rapidly as they approach and pass their 70s. But that's a different story ;-)
So the question is not a particular calling sequence or set of instructions is good, you need to look at the entire economics of the system - which to me begs the question of if the smartphone/tablet and ARM be the disruptor to INTEL*64 - time will tell.