Hi Holmes.
I'm not sure you're reading the article correctly. Although the authors do say that "attractiveness" is based more on processing than symmetry, they don't say that symmetry isn't a component of the ease of processing they noted. Given the ubiquity of image searching behavior (which is basically what they found) across the spectrum of the animal world in everything from insects to primates (for predation, predator avoidance, mate selection, etc), I would have been more surprised if humans didn't do the same. It IS interesting that they seem to have isolated the behavior, though.
Thus it appears that brain processes might create a general selective function which does not rely on specific evolutionary benefits.
This is a huge step beyond what the authors are claiming, however. Image searching has a quite valid evolutionary explanation that has been borne out through experimentation and observation. I'm not clear how you can make the statement that this "does not rely on specific evolutionary benefits". Perhaps you can clarify your argument here - I may be misunderstanding what you are saying.