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Adam, there are a few things about your model that might be affecting the outputs.

1- The unmet loads are significantly large, especially for the heating days. Because your model is in a heating-dominant region, this can significantly affect your energy use.

2- Also, the selected size for the mini-split was a 1-ton system, which seems to be very small for this building. After using the autosizing and adding an electric baseboard to the models with a mini-split system, you can see how the indoor temperature is increased and meets the thermostat setpoint temperature during the heating days. Also, total energy use increased.

Before:

After:

3- Compared to the DOE prototype buildings energy use, your total energy consumption is very small and it could be why changing the building envelope properties doesn't show a significant impact. I compared the last two scenarios after reducing the thermal resistance of walls and noticed that the energy use increased by about 10% (mainly because of the changes in heating loads). However, because the total energy use is small, the energy-saving does not look significant (about 1600 kWh reduction in energy use for 12 cents/kWh = 190 dollars).