if you look at the histogram. There's still room to brighten the image without losing any detail. It's just a bit hazy and needs more local contrast.

I haven't used Aperture but maybe there are similar parameters in Aperture's sharpening settings. You need to be able to control the radius of the sharpening effect. Large radius values create local contrast. ACR and Lightroom have a clarity parameter that does the same thing. Maybe also Aperture has it?