Two separate questions here. Addiing square footage (assuming its done professionally and following best practice guidelines (building codes, permits, etc.) should add value to your overall home. How much depends on what was done, where you live, and many other factors.
Using a window AC unit to heat and cool your home probably won't add value to your home. It's a convenience and lifestyle choice. Plus, if it is small and portable, it would be considered personal property, and not real property. Real property becomes part of the home. Personal property can be removed, and thus not appraised as part of the home (thus not adding value).
Hope this helps!