Its worth it.
But I would wait till Next-gen cards.
A GTX 570 would be enough to handle games till then
And SLI a GTX 570 will be not good. Because its a 1GB version.
Most games on eUltra 1080p cross 1GB of available VRAM.
So just wait it out with the 570? Well, I can play every game I throw at it so I guess I can wait a little more.