However, a lesser price duplex might attract more buyers (lower price range = more buyers).
Single family home has no neighbors - and privacy is appreciated by buyers.
It has a back/side/front yard - with no one telling you to match your flowers to the siding color, and
kids/dogs can run everywhere.
There is no "discussion" of when to change the roof or siding, or porch (if shared).
Your neighbor won't start defaulting on his mortgage - putting you in an unpleasant situation.
Sudden low resale of your neighbor won't decrease your property value.
Hope this helps,
Beachfront Realty, Inc.
In the Fairfax, Virginia, for instance, there's an area of 3/1.5 duplexes that sell, more or less, for $190,000-$230,000. You could go less than a mile away and find some single family homes, also 3/1.5 or so, same approximate age, selling for $100,000 more.
Again, that variation really depends on your locality and other factors. But you get the idea.
Hope that helps.