I vastly prefer the 6D to the 7D. However, what counts is which lenses you have now. If they are all crop lenses, then you are better off getting something like a 7D for a while, and perhaps begin to sell off your crop lenses until you're ready to get a full frame body, and begin investing in EF lenses.
The only other reason to get a 7D instead, is if you mostly shoot in very bright light, and you already have a terrific but perhaps pricey EF telephoto lens in the ~300mm range (that you are emotionally attached to and prefer to keep a while longer), and prefer the "reach" of that combination. And, you would rather not pay up for a longer lens...and also have to carry it around (which can be a very big deal).
For low light, I would forget the 7D. In a pinch it can work, of course...but it is a big compromise with its noise. Even the noise floor at ISO 800 is not very good...mostly luminance, with quite a bold grain. Chrominance sets in above that, and resolution begins to deteriorate fast. This is a debated topic, but an 18mp 7D, is not 18mp above ISO 1000. So there goes whatever "reach" advantage it had.
A friend of mine seems to think he is happy with his 70-200 f/2.8 ii, and his 7D. Franky I think that combo makes no sense, because the 7D is ideal for brighter light...and in bright light you certainly don't need the larger f/2.8 lens to carry around all day. For instance, he went to a car race and mostly used the 70-200 f/2.8. A waste of energy, it seems to me. The resulting shots all show very bright daylight...all could have been done with an f/4 lens, and sharpness would have been identical when closed to f/8 or smaller. His shots were great, though.
Obviously not everyone has the ideal combo of lenses and bodies, myself included.