The only reasonable APS-C advantage is the price.
Which is a very large advantage. At the risk of repeating myself: "A crop camera is the best/only way of optimizing the following combination of attributes (1) lower price, (2) higher frame rate and (3) smaller pixels (i.e., lots of "pixels per feather"). I currently own a 5D3 and 7D both of which were purchased in the last 6 months. (They replaced a 5D and 40D.) The 7D is used almost exclusively outdoors in comparatively good light with longer lenses to photograph things that move rapidly and unexpectedly. The 5D3 is used for everything else."
Notice the word "optimizing"
All I'm saying is that most of APS-C advantages are "synthetic" and $-related. Yes, price is a very big reason and for a non-professional enthusiast like me, having more than 1 DSLR body is not an option. I'd rather have one or two more lenses. FF can do everything as good or better than APS-C, no need to have both. If 5D3 had 46mp sensor, then you could crop 18mp image out of 46mp and it would be just as good as your 7D image and much better when you don't need to crop it. I'm sure it would be possible to get 2 more fps in crop-mode, if 5D3 had one.