I've never personally had a triple screen setup, but I have used them. I'd say the fact that I never bothered to get a triple screen setup for myself is quite telling. Honestly, a triple screen doesn't really do much for me; sure you can see a bit more to the sides, but it's hideously distorted, and you have two seams/creases in the view. It's is absolutely not immersive in the least, in my honest opinion.
VR, though... Tried it once, had to have it. Will never go back. Sure the effective resolution is a bit lower than a standard monitor, but honestly it doesn't make a damn bit of difference when you're racing, so it barely even registers as a negative to me. As for the screen door effect, you will only see it if you're looking for it. As soon as you get yourself into the race, you do not notice it at all.
VR has several major advantages over screens:
1. Ability to actually look around. You can look out your side windows. You can look at your mirrors. You can pile straight into another tree because you're staring at all the beautiful detail around you in the cockpit that you would never get to see in a 2D Screen. This exponentially increases your awareness in the car, and no matter how many screens you set up, it's just not the same.
2. Binocular vision. This is something that I really didn't think about beforehand, but real 3D from binocular vision is a complete revolution. Suddenly you can actually see how steep the hills are. Depth perception is perfect. Once you acclimate to it, you will become more consistent because your brain is no longer trying to interpret these things from incomplete data. You can see it, now, just like you would in real life. 2D screens are absolutely never going to be able to do this, it's physically impossible.
3. Immersion. Looking left/right by pressing a button is distracting and immersion breaking. You don't need to do that anymore, you just naturally turn your head. You look directly at your mirrors. You can do it just like you would in real life, which helps to really put you in the car. Additionally, no matter how many screens you have, you are always acutely aware that you're staring at a screen. You see your desk, you see your wheel, you see the wall behind your computer. That all pulls you out of the game. In VR, all you see is the game. Everything else ceases to exist. You feel like you're there.
Honestly, the move from a screen to VR is more impactful to the experience of racing than the move from a keyboard to a wheel. That's not hyperbole, either. I'm 100% serious about that. Even in its current GPU hogging, screen-door touting, low FPS state, VR is amazing.
Triple screens have never been good enough to get me to bother spending the money. VR is a must buy, imho.