In real combat, both quick and carefully aimed shots are useful depending on the situation, for at least two reasons. In situations such as an ambush, when the target does not see or is otherwise unaware of the firer, it is beneficial to hit it with the first shot, regardless or how long it may take to aim precisely, because after that the firer's position, if only approximately, will be made known to the enemy, who will now be prepared for fire from the same quarter and will take measures to neutralize the firer. This consideration can hardly be accounted for in the classic X-COM (but must be in the games it inspired).

The second reason is that snap shots are more effective at close range and aimed ones at long range. It happens because at short range the dispersion cone is much smaller than the target's angular area and aiming consists of pointing the weapon roughly at the target without the use of sights. The hit change is near 100% so the winner is the one who shorts first. At long range, however, the situation is reversed. The weapon must be aligned carefully to point at the small target and stabilized to narrow down the dispersion cone. The effect of distance is not uniform across all ranges but follows the behavior of the quantiles of the normal distribution.

Precise aiming takes a certain time determined by the weapon and the firer after which accuracy reaches a plateau and then starts to degrade due to fatigue. During the effective aiming stage the rate of accuracy increase is highest at the beginning and becomes lower at it approaches the plateau, but in the end the probability of defeating a remote target is improved out of all proportion with regard to the time spent aiming.

That being said, I don't think serious improvement is possible unless someone can change the hit-chance formula so that it will approximate, if loosely, the varying effect of distance at different ranges described above. As distance increases the effectiveness of auto- and snap shots should become lower compared to that of an aimed shot.