I consider post processing to be in three parts
1) RAW adjustments
2) DAM
3) Extended adjustments and edits
Often items 1 and 2 are together and items like Aperture and Lightroom (and some other software to some extent like Capture One Pro).
If you are just now deciding which RAW / DAM software to get, consider first which one does best with your camera files and then check to see if the work flow is reasonable for extended adjustments (Photoshop, Pixelmator, GIMP etc.).
If you don't own Aperture now, you might just either wait for the new "Photos" by Apple and see what it has to offer or as many are doing, going over to Lightroom. Aperture wont be getting soon any more upgrades. It still will function well, take 3rd party plug ins but again, no upgrades.
While I use Capture One and Photoshop CS6 for my purposes, I often set up friends with either Lightroom or Aperture and Pixelmator. They seem to be very happy with the combo. There are of course other software that you might consider such as DXO. In your shoes, I would be more concerned with RAW processing and DAM than extended edits as related in Pixelmator and Photoshop or GIMP. (I'll just say that for the price Pixelmator is quite amazing in its latest incarnation/version.)