You guys will probably think I'm weird, but depending on how improved the 70D sensor turns out, I'm thinking about selling my 6D and going to two or three crop bodies. (Downgrading from FF to crop? zomg!)
I love the sensor in the 6D, but it looks like everything else about the 70D is shaping up to be better than it's bigger FF brother. Faster flash sync, better autofocus, higher fps, articulated screen, built-in flash... I can't think of anything on the 6D that is better besides the sensor (don't use GPS). Switching back to APS-C also means cheaper bodies and lenses, which means I can afford more bodies and lenses! (f/1.8 Sigma zoom anybody?)
I would trade some sensor performance for a bit of everything else. It looks like the 70D is going to offer a lot of everything else.
Nothing at all weird about that. It's just a case of what your style happens to be. Full frame is not better
than APS-C, it's just different. If you don't shoot at high ISOs, if you are more of an "F64" shooter than a wide open romantic bokeh type, if you don't routinely print larger than 2 x 3 feet, then the differences may not be worth the cost.
It is impossible to determine from a well-made print if it was shot on APS-C or full-frame. Much of the supposed "image quality" differences that full frame shooters think they see can be ascribed to confirmation bias.
Choose whatever works for your style and your budget and don't be intimidated.
Finally, remember the cardinal rule: "if you want to take more interesting pictures, stand in front of more interesting things."