All that said I love older homes and have owned a few  however accidently digging up your septic or opening a wall to find it used to be a shed teaches you to be cautious.

Sometimes its best if you just buy an empty lot but other times it may prove advantageous to do a remodel leaving the foundation and one wall up.

What I was saying is that I have hit many walls, and I haven't given up.

v=IPM8OR6W6WE- problem valley in a roof, that keeps accumulating leaves and easily leaks- Commercial property that attracts graffiti artists - paint won't stick- Walls in bathrooms that don't have great ventilationWhat else can you think of.....?

What is the rehab cost difference in leaving it as a duplex vs tearing down the walls and reconstructing it?

The electrical runs are fished through walls. 

Pex can be "fished" through walls just like electric wiring.

I know reputation is everything in this business, but I also think that if you throw enough mud against a wall somethings gonna stick.

Measure the wall square footage, they go around $2-2.50/sf.

Add amenities, landscaping, any other items such as for condos, fire walls, road construction, etc.