2-4 family dwellings can many times be frustrating, in that there may be very few, or none, such similar sales to do a 1025 form, 2-4 family. as a single family with adu, i agree it is, the value may come in higher because there are more sales to pick from. with zoning approved you only need 1 adu comp, without zoning approval you need 2 adu comps, as per fannie guidelines. FHA somewhat follows fannie guidelines. you can always have the electric meter removed for that adu, thus no utilities provided. if you want it so badly, put the interior entrance back in, or remove the kitchen.
if you love the house, do you really need that adu for now, at least.