Rule: if the utility of a second bike exceeds the value or amount received from the sale of the first bike then keep it.
So storage and finances can trump this rule.
While a bit if a luxury, found having second road bike is good when new bike is in shop or to give the bike a rest. I ride two 30 mile recovery rides a week at about 16 MPH or less and the second bike is great. This allows newer bike for bigger and faster rides and spreads wear and tear on tires, chains, dérailleurs etc.
So yes I see the value of keeping a second bike. Also may end up getting a Summer place which would be a time to bring bike there to have some use.
Kind of like a second refrigerator. Don't need one but my you like having it at various times.