Isn't it pretty badass to be able to sprint in three-inch stilettos, though? (I personally think high heels look silly, but I'd be impressed by anyone who could sprint in them without extreme risk of ankle injury.)

The point, which I don't think you conveyed very clearly here, is that sexually dimorphic characteristics which have the potential to impair the fitness of a mate, but which have been successfully overcome, are an authentic indicator of mate quality.

In the case of any specific trait in any specific species--the peacock's tail, for instance--it's unwise to assume that this must be the case, given the variety of alternative explanations. (For instance: the tail is an example of unbounded sexual selection on behalf of peahens, where attraction to a sexually dimorphic characteristic turns out to be less evolutionarily pliable than the characteristic itself, sending the species gallivanting off into satisfying the giant-tail-fetish that peahens accidentally acquired as part of the mate-identification system that was selected for in their ancestors without any need for selection for "hey, wait, that's crazy, that's way too much!".)

However, if you ask: what are the reproductive habits of birds, say, with the most outlandish and hampering male plumage, and you generally find a strong trend towards exactly what you'd expect for the case of authentically-fit-because-it's-actually-hampering-males: polygamy, little/no investment of males in offspring, or at least a high degree of "extra-pair parentage" (i.e. infidelity). In all of these cases, the fitness of the females is not impacted by the less-fit males getting eaten and the more-fit ones being pretty useless aside from being awesome-feather-displays. They "know" they're getting the good genes, so they have no reason to choose anything but the most spectacular authentically fit males (whose genes will help ensure their female offspring are actually fit, and their male offspring will be better equipped to play the same game). None of the other explanations for extreme sexually dimorphic characteristics really explain this widespread pattern at all. So we can have a high degree of confidence that sending an authentic fitness signal is sometimes exactly what is going on, even if in any individual case we should retain a healthy degree of skepticism.

When applied to humans, the approach of evolutionary psychology has a tremendous difficulty in surpassing the "just so story challenge" for a variety of reasons including our extreme behavioral pliability and the lack of any extant closely-related species. It's not necessarily completely impossible, but the degree of evidence necessary to provide a compelling account is rarely met (and many times it seems as though it would be impossible to meet it). Furthermore, there's a disturbing tendency to exacerbate overinterpretation of poor-quality evidence by committing the naturalistic fallacy.

It's highly appropriate for scientists ("scientists"?--it isn't always clear that evolutionary psychology in practice meets the minimum criteria to be a science as opposed to, say, aspiring to be a science) in the field, first and foremost, and others looking on, secondarily, to insist that they keep themselves honest and the conclusions appropriately tentative.