There are actually a lot of very good articles available via MSDN and other sources that explain exactly how Full-Text Catalog information is gathered, processed, stored, and queried.  Unfortunately most articles give this info out in small bite-sized pieces, meaning you have to scour the Internet to piece together bits and pieces from all over.  SQL Server MVP Hilary Cotter is a great person to Google if you want specific information about how SQL FTS works.  He knows more about SQL FTS than probably anyone outside of Redmond, and he frequently writes and contributes to FTS articles and books.

The internal tables you reference store some metadata about the full-text indexes/catalogs (basically ID number mappings/references) but they are not 'the' full-text indexes/catalogs:  http://msdn2.microsoft.com/en-us/library/ms366343.aspx

I agree with your sentiment that reinventing the wheel without some additional gain is not worth the effort, except maybe in a purely academic setting where your grades depend on how well you reinvent the wheel.