3D isn't really dead however, it's in a process of "innovation". From now on, VR headsets like Oculus Rift will be using 3D, coming out by the end of this year, so yes, if you want 3D, u are free to invest... I would recommend you take a 2-way SLI cards. Palmer was saying on a conference that you will need to achieve minimum of 60FPS on 3D, so watch out! You might find it challenging!
However, with Oculus Rift, Nvidia, want or not, will have to start working on their 3D vision since Oculus is gonna be this year for gamers! I know they got under Facebook, but for me - I just wanna play VR games and that's it. Facebook will probably put ads as "in-game" graphics/items of some sort as I heard, that's not as bad as having ads stacked all over around the screen at your face, which is horrible...
So yup, if you've got the funds, just go get it. Also DX12 is coming next year and it seems performance will be highly increased, and I hope 3D too...it's NOT dead!