Just to update on my findings today (after setting my Aperture export color space to Adobe RGB (1998)), I've tested all of the combinations and concluded some disturbing things about the way Aperture previews files.
Essentially, my mistake when I posted was that I assumed the issue was with the file that was being generated when I shuttled an image to Photoshop for cleaning. As it turns out, the new image is faithfully accurate to how my photo *really* appears. I realized this when I was in zoom mode and jumped between the two copies of the file.
Zoomed in, the images are identical. The original image has the same harsh tones as the copy (which makes sense). Zoomed out to fit the whole image on my screen, the preview on the original is different. I've replicated this phenomena for about a dozen photos, both color and greyscale.
The weird part is that it only seems to happen if I have changed the levels of the photo (histogram) or enabled edge sharpening. It's like those two functions are not properly rendered by the preview you see when zoomed out.
To be clear, I've regenerated the previews and even tested with my preview quality set to 0 (terrible) to verify.
If you're zoomed to fit on the screen and you've changed your curves or used edge sharpening, the image you see is NOT the image that you'll end up with.
I'm perturbed and a little heartbroken thinking about the hundreds of hours that I've spent preparing my work and then always quietly being disappointed with the digital output. I chalked it up to JPG rendering. Now I'm faced with either finding a workaround (likely doubling the effort required by my workflow) or just live with it.