A 3D simulation would represent a big improvement for formation flying or landing and taking off, but not so much for flying at altitude for obvious reasons.
But the absence of body accelerations in a simulator is a big obstacle standing in the way of realism. Big, expensive simulators have a cockpit mounted on hydraulic actuators to partially address this issue -- the cockpit moves around to provide some accelerations and try to improve the subjective sense of being in motion.
