I seek opinions from my learned colleagues regarding whether or...

I seek opinions from my learned colleagues regarding whether or not to put a granny flat onto the back of my investment property.

1. Will the granny flat improve the property value relevant to the total investment when considered separately?

2. If I sell the property in the future how does one assess the value. Would it be based on straight land plus improvements or on cash flow.

I am ready to go with the granny flat but am starting to get cold feet. Please tell me what you think.