I think the answer is that it depends what you use Photoshop for. From my understanding Aperture and Adobe's Lightroom, provide photo management and some Photoshop like features and both allow non-destructive editing. However neither is billed as a Photoshop replacement.
The consensus I've heard is that for alot of common adjustments, you can can do them in Aperture or Lightroom but for more complex stuff, you might want to keep Photoshop around.
I don't know much about the latest versions of Aperture or Lightroom, but initially many felt Aperture was a resource hog and pretty slow on all but the fastest most RAM loaded desktop Macs, however this might have changed.
In any case, get the cross-upgrade for Photoshop just to have it. I wouldn't run Photoshop or any other resource intensive application through the Mac virtualization tools (Parallels or VMWare or Bootcamp) it's just not as fast particularly as you can get a native version.
Welcome to Mac. The primary advantage of getting a Mac IS NOT that it can run Windows and OS X on the same machine althoughthat's nice, it's that it runs OS X.
You spend less time screwing around with your computer and more time doing whatever you sat down to do.