Was that stupid too?
If you can actually get it sold for that price then go ahead. But you will still need to add money to get the 1070.
All over Craiglists its the same people over and over posting their RX gpus for $300-400 each, and they repost everyday and not a single one sold. Aside from a few lucky people, most people can't sell their RX gpus for $400.
Even if I could sell my RX 480 for the exact same price of a NVIDIA GTX 1070, I rather not deal with the headache of eBay/Craiglist people. And its not worth the hassle to remove GPUs, add GPUs, configure GPUs, etc. I'm not a newbie, been mining for way too long and "assembling" rigs is no longer fun for me, its boring.
In the end I don't really care about making an extra $50 per GPU per year.
Like the previous poster said, the real money is in trading cryptos.