I would strongly advise against going into the database world half cocked. You make a program that is not easily adapted and it sucks but you can deal with it. Do it with a database, especially one you aim to have each person maintain their own copy of, and you are in for a nightmare a year or so down the line.
If nothing else go have a look in the site suggestions forum and see all the long and detailed discussions on the changes to a few categories -- basically any of the suggestions/points of discussion could be added to the site layout in minutes at best but I am sure the list I am sure the list of unpleasant things Nightcrawler would sooner do than make a hasty change like that would be quite long indeed; most of those are just refinements to categories as well, mess up the overall layout (aka database schema) and you might as well not have bothered.
This then sounds like a job for sqlite, it is not quite big boy SQL but it should be more than capable of doing what you want. I forget the programs I used to use with them (I have mainly been dealing with mysql for websites of late) but they should make for something almost exactly like what you want ( http://sourceforge.net/projects/sqlitebrowser/
should be a good start). SQL is not very visual but it is very human readable for basic queries. Alas most of the things I have for SQL are paid books and I would rather not link w3schools (though you could do worse I guess).
Fully formatted documents might be a stretch. Nicely formatted text files, csv files and more besides are a different matter entirely. On the flip side I have never really had call to interface between a sqlite database and an office suite and fumbling with spreadsheets and more besides over the years they do appear to have something in that world (see also ODBC)