I have a Rift, three screens and TrackIR, so I'll give you my opinion for what it is worth...
TL;DR: Get a rift or head tracking. Three screens are fine, but won't add that much.
Three screens are good. I bought mine for iRacing. In that, it is a major help as iRacing properly supports three screens (it renders them separately). It allows you to have a natural FOV and also look into corners etc. In most games, it isn't so helpful. Most of the time the image gets distorted on the side monitors - it adds some periphery vision, but that is about all. On many games, it is not usable as the game isn't written to support it at all (e.g. the gui ends up on opposite ends of your three monitors and is a pain in the backside). In things like flight sims, your vertical FOV is usually more important than the horizontal. ED is a bit of both, but I would say it is more vertical than horizontal. Three screens is nice to have, but I wouldn't advise anyone to go and blow a load of money on three screens for ED alone as it doesn't add a lot.
Far more effective would be spending the money on Track IR or similar. It is far from perfect, but is certainly helpful and likely a much cheaper solution overall. I played for some time with three screens and Track IR and the result is good. You gain a lot from being able to track targets and look at the holoscreen menus. Three screens will help a little with TrackIR, but not much - you still end up moving your eyes as you move your head, as the focus is the centre of your centre screen, hence 'looking' at the side holographic menus brings them to the centre of the screen! You still only gain periphery vision.
But the Rift... well, I just don't do either ED or iRacing on three screens any more. The experience is so much better. It can't really be described, but you are just there. Many others have pointed out the low res, screen-door etc so I'll just say on this - ignore Dr Zachary. I can understand his personal opinions about the resolution not being good enough for him etc, but he seems overly keen to find 'negative points for the rift'. For me, it is fine (I can read text with no problem, so I don't know what the issue is for others there). I have no problems with eye strain, even after using if for hours. It is uncomfortable where it presses against my large nose. I am extremely prone to motion sickness, but in ED I don't get sick. I may have the odd moment where my stomach flips, but I never get sick. It is intense. The head tracking, sense of depth, of size, scale and detail (in many ways you see more detail in 3d low res than 2d high res) massively outweigh the down-sides for me. IMPORTANT: You will need a really good rig to run ED in the Rift. It is far more demanding than three screens, not least because your experience in the Rift is very sensitive to frame rate. In 2d, if you momentarily drop to 40fps it doesn't really matter. In the Rift, the experience is awful and can make you feel ill in seconds. My 7850 2gb is enough. Just.
So, what should you do? For me personally, I'd say get a Rift. You can probably get most of your money back on eBay if you find it isn't for you. Otherwise, get head tracking and wait until CV1. Three screens? Hmmm - I'd say ED is not the 'killer' use that justifies the expense.
I highly recommend VoiceAttack, whichever route you go down.