I know your question is addressed to homeowners and buyers only, but I hope you will welcome comments from realtors who are dealing with many buyers and sellers, and who have listened to what matters most to them
Before you do any remodeling, you should also review what improvements rate the highest payback. Here's a link to a feature of Remodeling magazine online where you can select the region/area of your properties, and see what is favored in each.
Of utmost importance are improvements in kitchen and baths, and the master bedrooms.
Also....if you have hardwood floors under carpet, by all means, uncover them and have the floors refinished. Buyers are always looking for this feature. But if you're thinking of changing floor coverings, do consider bamboo floors --- it's number one on the list of renewable resources for floors.
For kitchens, do consider changing out old appliances for energy-efficient ones.
For outdoor landscaping, research Xeriscape which is probably the most earth-friendly style of landscaping.