You need to put up some examples of what can be done by this service. Something visitors can interact with without registering is ideal to convince them to register.
This is linked off the front page, but could certainly be more prominent (as another commenter said)
But I don't think showing the spreadsheet in the API docs is so useful; the idea is to present a clean API to the users, and they don't even need to know that the data was originally from a spreadsheet.