LtMatt's spot on - I went from 2 x 7970's to 2 x 290's on Eyefinity and the hardware frame rate pacing in the 290's makes a WORLD of difference for Crossfire + Eyefinity. It's so much smoother I am VERY glad I made the swap. That said, if AMD can come through and produce a frame rate pacing software solution for the 7xxx series, then you're better off with 2 x 7950's as the extra cash for 290's won't be worth it.
As to whether Eyefinity is worth it is a personal thing, I'm afraid. I have been running 3 screens since 2009/2010 with a 5870 and couldn't go back to 1 screen now, no matter the size. Two of my friends have bought 3 screen setups after playing with mine. However, my youngest spends loads of time on my PC and only plays on one screen as he finds the other screens too distracting in game. Personally, I find playing on 1 difficult as it feels like I'm wearing blinkers.

Best suggestion is get in front of a 3 screen setup if you can and try it, some love it, some just don't get on with it. If you're close to me you're welcome to come and try my rig sometime.