A little investigation and some math would answer the question. A nice home with an ADU would be worth some very serious money, and stage well. Build the ADU first, then live in it while building the house.Yeah it could go either way. At minimum the house needs gutted to the studs in the kitchen and bath(s), full rewire, full repipe, full HVAC, and then you're still stuck with the 1912 or whatever floor plan of many small rooms. That's assuming the foundation is in good shape. In Berkeley I just don't see too many people paying for the land then constraining themselves to the floor plan when they're replacing 80% of the building anyway. There's also the new zoning allowing multiple dwellings to consider as well.
Berkeley is a tough place to work though. I promised myself I'd never take another Berkeley project after going through the last one.