Usually in heavy-ion experiments, results are given in terms of momentum space variables
However, detectors are composed of different cells and hence there is some finite resolution on the position of detected particles.
Is this correct? If so, why is it this information not used?
It is maximally used to calculate the values for energy-momentum for the events under study.
Here is a simple detector of particle physics:
It shows one event in a bubble chamber , the beam entering from below, and the point of interaction, your space coordinate, is where the tracks diverge. The tracks follow the magnetic field classical solutions, so their momenta can be calculated. The backward pion decaying to a muon and then to an electron give another two space points. The accuracy of measurement of space points is important for measuring the momenta of the track, and the ionization which can define the particle mass.
The reason that it is the momenta that are important is because there are no space dimension conservation laws that can be used in the quantum mechanical calculations to describe the reaction. Energy and momentum conservation though allow to determine the energy and momentum of this individual event.
An accumulation of such events can be described with a quantum mechanical model, where energy and momentum conservation holds. An accumulation of space points measured cannot be simply predicted with quantum mechanical theories.
The complicated heavy ion detectors are following the same logic. Measure the energy and momentum of outgoing tracks, to be fitted with the model and check the theoretical calculation whether correct or whether a change of model would be needed.