Where does the walkway lead to, and does it border or cut through the subject property? A park or nice commons area?
I know that in my area it's often considered a bonus if you side or back to a walkway or bikepath that leads to greener pastures.
The answer is Yes, No and Maybe. The private rear lot - was it separated from the original lot at one time; is it a separate parcel under the same ownership as the subject? Why do you have a walkway - is this the only access? Was it required by law when the properties were platted or split apart? And finally, does it affect value and can you prove it?
It may be that if the overall utility of the property is not affected other than the fact that someone has an easement across one side of the property, then the loss in value would be the differential in site values for size since you have effectively lost part of the site.
I would think that the key to a good report and how to handle the easement is to describe the easement (who, what, when, where, and why). This will tell you how to handle the easement.
I don't see easements as either. Easements should apply to the site value which does not depreciate. However, if the easement affects the use of the property, then a case can be made for a different highest and best use. If the easement reduces the usability then a functional ob. might apply that relates to building an inappropriate improvement near such an easement.