I have some one that is willing to buy my current computer for 800 so I would just be paying the 400$ difference.
$800 for a used computer? That's gotta be a profit. Good for you.
One thing: 12GB of RAM...does the board support tri-channel? If it has 4 slots, then it most likely is a dual channel board, so I would go with 8GB or take the plunge and do 16 (but 16 is really unnecessary based on the objective of the computer).
As the title says do you all think that it would be worth the upgrade. The goal is to play next gen games on high settings.
$400 to move from your old computer to the new one? It's a no brainer - not only will you see a difference, but you should be good on most games coming out in the near future.
Hope this helps.