When your spreadsheet start to hit its limits, what options are open to you? Perhaps the best option is to consider the conversion of your spreadsheet to a database solution. Relational databases became viable not too long after the spreadsheet was well-entrenched as the affordable and quick means of gathering data and performing calculations.
You'll need to develop good marketing material. Things like demo videos, which you can find plenty examples on YouTube, screenshots, and keyword rich descriptive text help people find your spreadsheet and communicate the value that sets yours a level above the rest. Excelville.com actually allows you to upload your spreadsheet with all of this marketing material in an easily searchable and user friendly website.
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.
One user at a time : In the instance where there are a number of people required to work on a spreadsheet, they can only access it when no-one else is working on it.