I honestly don't think I would miss my crop cameras (7D & 10D) for my FF cameras. Then again, I don't think I'd miss my FF cameras for my crop cameras!
I think it's more the quality of the photos them self that wants me to keep what I have. Love the 7D as well as my 5DMKII, and that is why I keep them.
If I am going off to "play" with my cameras, no matter what I might be interested in shooting, I usually bring the 5DMKII AND the 7D. If I am asked to shoot something, such as a wedding or family photos (or such) I'll usually leave the 7D at home and use a different lens on each of my 5DMKII's
Having said that, I've never really given a lot of attention to Crop vs. FF ... to me, it's more of "Which lens will get me the better shot with THIS CAMERA?" THIS CAMERA being the one I have at THAT moment, be it the 5DMKII, 7D, 5D, 10D or even my uhhh, 35mm camera