Basements are hidden gems. They offer unique expansion opportunity and are not limited to one specific purpose. You can convert them into anything you feel necessary for your house:
office with an extra bathroom, bar, huge family room with a fireplace , playground for you kids as fancy as recording studio, even a separate apartment if zoning and building codes allow that type of conversion.
Picking the right use for the basement will dramatically enhance your quality of living and functionality of your dwelling, making it more interesting to future buyers.
This is probably the least expansive way to increase the living/working area of your house.