The Town assesor will use the foot print for the property as their starting point. In other words, if the footprint is 48x28, and your living space is comprised within that footprint, then you have a 1,344 sqft home. Now, add to that a second floor and you have doubled your sqft living area to 2,688 sq ft. A basement will be calculated and added to the total living area by measuring the "living" area in it. In other words, the mechanical room will not be counted, therefore the basement, while still part of that foot print, will be measured by actual living space. The same goes for an attic.
Curb appeal is great in the eyes of a prospective buyer, as long as the neighborhood follows your lead. A bank appraiser will look at the overall condition of the street to help determine value, the value will mostly be determined by the condition of your home and area where it's located. The Banks will only use the appraisers estimate to determine value.
A thorough CMA (Comparative Market Analysis) will give you a vey good estimate of your homes value and who your competition is.
If you need further assistance, let me know.