Yes most have 2 separate screens, but not all support 3D (the screens are fed the same image).
I have already flown a 3D setup with 2 cameras, it's... quite nice, but it's not like day and night. It adds a little something but isn't really worth it IMO.
The problem is that we fly with rather wide angle lenses to have a pretty realistic general view, and this causes the depth effect to only work for close objects. The setup I flew had the cameras on each wingtip to have about 1m separation instead of the usual natural separation, to amplify the effect - but even so it works only with objects up to 20-30m distance. And it also exaggerates it so much for closer objects that for landing you feel like you have one eye on each side of the runway
Head tracking adds more IMO.