Well should I sell my 570 right now and get the 670? Because my 570 won't be worth that much later on...
And also any thoughts on 2 monitors if im gaming on only one?
If you want to sell your 570, then selling it ASAP would be a good idea. It is my recommendation.
I don't recommend dual-monitor gaming. Odd numbers of monitors (one or three) are generally better because you don't have a bezel in the middle of your screen.