It's really only worth it if you're already on a higher-end GPU (GTX 770 minimum I'd say) as it essentially halves your framerates, for some of the better-looking games out there, you'll absolutely need at least two GPUs to run with acceptable performance. Also, despite the fact that (like SLI) not every game supports it, if you're willing to do some work, you can vastly improve or even fix 3D compatibility in many games with the files available at
Helix Mod.
In short, is it worth moving up to a 3D setup by buying all new GPU(s), displays AND the 3D Vision 2 kit? I'd have to say honestly no, and this is coming from someone who likes 3D enough to be running triple screen 3D Surround. Is it worth trying out if you already have the necessary hardware and just need the monitor? Yes, it definitely adds a lot to the immersion (Metro, Tomb Raider and Crysis are particularly amazing). And if you end up not caring for 3D, you'll at least have a nice new 120/144hz monitor that will end up improving your experience in fast-paced games by providing greatly improved response times, which is always a plus.