As per my views - If you intend to use your new projector for at least 4-5 years, then 3D is a must. You will feel "left out" otherwise.
That said, 3D technology is still maturing and therefore its highly probable that 3D engine being used by today's PJs may become outdated by next year and so on. You should make your mind and mentally accept this possibility before taking the plunge.
I had same dilemma. In the end, I just bought a 2D 720p PJ. I will use it for next 2 years and then make the 3D 1080p jump.