Many spreadsheet applications nowadays have functionality above and beyond the traditional, offering a variety of charts, look-up tables, databases and more functionality than can be mentioned here.
Financial templates are highly complex and they deal with very large and advanced calculations. These spreadsheets are used in mortgage, loans, and property investments and so on.
You might be providing an extremely valuable service to many, many people. Your spreadsheet might free up peoples time from boring and tedious administrative work to spend more time doing things they love. It might help keep businesses above water or help them reach for new heights. Your spreadsheet might even help to create jobs or at least keep people employed.
Using Excelville.com, there are no costs associated with selling spreadsheets and you don't need to build and manage a separate site, which works out pretty well. Whatever path you take, I wish you the best of luck. Leave a comment and let me know how things are going for you.