As I was saying, if the residential use remains legal, even as a non-conforming use under the current zoning, then chances are pretty high that it remains the HBU. Not only would the different use have to be worth more than the existing use, it would have to be worth so much more that there's a sizable profit to be made for making the conversion improvements.
The difference between the two uses would not just be limited to the hard costs. Otherwise the buyer would have no incentive to take the risks and go to the hassle of dealing with the remodel and the X factor - that element of the unknown that invariably jumps up to bite entrepreneurs when they least expect it.
As an example: If the costs for paving a parking lot and marking a handicap stall, converting the bath to an ADA restroom and installing some additional electrical or data lines totalled out at $15,000 and your "residential value" is $185,000, the "as completed" value would probably have to exceed $225,000 in order to provide the contingency and the profit incentive necessary to motivate a buyer to do this remodel rather than buying a competing office unit. Anything less than that and an office buyer would have no reason to get involved.
I think that once you get a look at the commercial sales data that would be the comps for such a property you'll be able to see right away whether there's a big difference on a price/SqFt basis. If there's not much demand for such properties then that only increases the risks involved (and the necessary profit margin), regardless of any price differentials.
The challenge for you may be in obtaining those sales data. If you don't normally run in those circles you may have a tough time finding the data.