Summary: Canon barely made much improvement to its APS-C sensor except for the small increase in megapixels. The Nikon D7100 and Sony A77 outperforms the Canon 70D.
Considering how big Canon is, I can't believe the gap between Canon's sensors and its competitors are growing. How is this possible? The Canon 70D's successor will not be released until 2015/2016, which means that its APS-C sensors will have essentially stagnated for 5-6 years.
I guess the answer is pretty obvious here. If someone doesn't need the features of the 70D (i.e. Dual Pixel AF), then there's no point to upgrade from the 60D since the 70D barely outperforms the 60D's sensor.