Other than those two things (re-printed below from the release notes), there are no other changes between 5.5.0 and 5.6.0. So, as you've said, no reason to update if you're not using that particular engine sensor (unlikely - it's a rare one) and if your compass is calibrated well.
[EFIS] Fixed: Magnetic heading calibration no longer sensitive to flight attitudes that are signifigantly different than those experienced in level flight. This primarily resulted in less than optimal calibrations in some taildragger aircraft. Performance will not change until a heading calibration is performed after an upgrade to 5.6.0.
[EMS] Fixed: Sensor type 10 sensor characterization for UMA 1BX Oil Temperature sensors.