The reason I use carriage spacers is that I am using Igus joints, and without them the rod ends foul the carriages and the effector. The Traxxas joints don't need them because they already have a flange that spaces the joint from the other parts.
I suggest you measure the Z probe trigger height at the G32 probe points, and also check whether any variation is due to effector tilt. There are a few of ways of checking for effector tilt. One is to mount a bulls-eye spirit level on the effector. Another is to lower the nozzle until it touches the bed or grips a sheet of paper, then use feeler gauges to measure the height of the bottom edge of the IR sensor above the bed. If there is no tilt and the bed is flat, the height should be constant regardless of XY position.