Just a footnote: people respond to facial symmetry very positively. In psychological tests, symmetrical faces are considered prettier than ones that are not, most likely because symmetry is a sign of genetic health. The stormtrooper helmet, were it truly symmetrical, would probably not convey quite the sense of subliminal menace that it does in its current misshapen form.
I'm in general agreement with the post's author that the filmmakers were shooting for an ideal that they lacked the funds or technology to reach completely, but I think that, in this particular case, the movie benefited from it. In fact, I think that one of the real advantages of practical (as opposed to digital) effects is that you end up having to make design compromises that enhance the overall realism of the effect. It's the girl-next-door syndrome applied to imaginary worlds. If they're too perfect, you don't believe they are real.