It is entirely too difficult to do what your trying to do, I think you need to be more concerned with the actual comp values of the particular neighborhoods your looking into. If you take an 1800 sq. ft. home that is loaded and an identical 1800 sq. ft. home that is bare and they are side by side in the same neighborhood, how can you compare sq. footage pricing? Because they are two different products. Feel free to contact if you have questions regarding this.
Newer homes have the most current designs, while older homes have wonderful charm...but as the old saying goes it's "location, location, location." Instead of just looking at the price per sq. ft. in general, I would recommend contacting a realtor and requesting a Comparative Market Analysis (CMA) for the particular area(s) you are interested in. Your realtor should be able to provide a CMA for any specific subdivision, so that you can look at the prices of the homes for sale and compare them to the prices that homes actually sold for recently. That will really be your best indicator of what a home is worth.
If you have any other questions, please don't hesitate to call me at 214-418-0180. I am happy to help.
Coldwell Banker, Jane Henry Realtors