As I wrote elsewhere, I have both Aperture and Lightroom, have had them both since before they were v1.0. I used to use Aperture for specific things that LR didn't support, as I prefer the way LR works. But in the past three years, that use has gone to nil.
In all cases, it's best to keep your workflow agnostic of a specific tool as best you can. Some things don't survive and better things come along—happened in film just as it does in digital. You should always be in a position to take best advantage of whatever is available. For instance, I simply wouldn't use Aperture for anything serious until I could always reference my original photos rather than embed them in its proprietary data structures. And whenever I "finish" a photo, with either, I export it to a "finished work" repository as a full rez, 16bit per component TIFF file to 'future proof' my labors. Relying on any specific application to be around forever has always seemed a foolish thing to do.
I'll be interested to see what Photos offers, both at first and later as it is developed. I hope it is a quantum jump beyond iPhoto, as iPhoto has always driven me a little nutty with its weirdnesses from its earliest days to the present.
Meanwhile, I just bought another ten packs of Impossible film for my Polaroids. If I get good enough at getting the results I want from them, my photo image processing needs become many many times simpler. Same for using the in-camera JPEG engines of my digital cameras.
There are always alternatives to work with ...
G