What do you need from the 80D that the 70D lacks? Do you find yourself limited by the megapixel count? By the lack of f/8 focus points? The number of focus points? 60Hz vs 30Hz 1080p footage? Flicker detection? Only consider the things that you really want/need, not all the improvements. Do you really need more megapixels? Likely not, unless you're often focal length limited, in which case it can help (just like the 5Ds). Only consider the things that have an actual "value" to you. 60Hz vs 30Hz 1080p? Not a selling point to me... but you do lots of video. Do you wish you could use an extender on a 400mm f/5.6? If so, the f/8 focus points are a bonus to you, but again, not to me.
Once you have the list, that's your "pros" list. Real reasons to upgrade.
Now, what can you sell your 70D for, to use toward the 80D purchase? Did you pick up an 18-135 STM kit? Perhaps you want the new nano. It's faster. Consider the price difference of the new kit vs. sale of your old kit.
The price difference is your cons list. It's the only real reason to not upgrade.
Now, do the pros outweigh the cons to you? That depends entirely on how much *you* personally value each of the items on *your* pros list.