Thanks for the feedback everyone.
I think I'm going to give it a shot in the next couple weeks. My walls are 2x4, so existing insulation is R-13. The stuff I linked above will add an additional R-5, so R-18 total. But from what I understand the greatest benefit is in the air sealing... will make sure to tape all the seams and seal any gaps with spray foam.
If an inspector has an issue with it, I can deal with that when we get there.
Next phase will be to air seal and then add some blown in insulation to the horizontal ceiling surfaces. My hope is that when it's said and done I can run the heat downstairs (heat pump) and not need the upstairs unit (resistance heat) to kick in at all.