Upload & Sell: On
A number of people regard the 7D and the 5D2 as being complementary cameras. As you know, the 7D works well for sports - a good AF system, faster burst shooting, the (arguable) advantage of "reach" from a given focal length on the cropped sensor body and so forth. The 5D2 offers the potential of better resolution, a larger range of usable apertures, potentially narrower DOF if you need it, and so forth. (A lot of this is the "more versatility" you mentioned in your post.)
There are also good reasons to have more than one camera body. Sometimes things break, and with the second body you aren't stopped in your tracks. In addition, you can have two lenses fitted to the two bodies, and perhaps move more quickly from one sort of subject/shot to another.
Especially if you already have the 7D, the 5D2 is an excellent camera that can produce image quality that equals that of the newer 5D3.