Since your home is most likely your biggest investment, you should first determine if you are doing it to sell or doing it to live in. If you're doing it to live in, it has little to do with the actual investment and more to do with what you enjoy. If you enjoy entertaining and you don't have enough entertainment area or the proper type of entertainment area, then build it in the basement.
If you're doing it to add value to your home, then get local comparables in your neighborhood from a realtor to see if it makes sense or look online at zillow.com. They are pretty vague and less accurate though.
No matter what the reason is you are contemplating refinishing your basement, keep in mind that it is the least expensive additional space you will find around your home. We have done many basement remodels and our customers have been amazed at how inexpensive it can be. Before you do anything though, ensure it's as watertight as possible. Your experienced contractor should know this and be able to guide you throught the process.
Owner-Moveout Makeovers-Palatine, IL