I sort of agree, but if you consider 2000ad and the Judge Dredd Megazine, and everything that is available around those titles as background material, there is plenty.
For the Dredd RPG, there is also this fact;
Every X-Files episode, and virtually any horror / sci-fi / thriller movie or book is an easily converted JDRPG scenario.
Judge Dredd as an RPG is so easy to fit virtually any modern or near future story idea to, once you are comfortable with the set-up of Justice Department.
The already released Rookies Guides are more than enough to last for years of playing. I recommend the Rookies Guides to; Psionics, Block Wars, Justice Deparment and Crazes as must haves, with the others as highly desirable. The published scenario's are also superb.
I'd love to see Mongoose publish more stuff, especially because Judge Dredd is such a rich rolepaying universe - far richer and more diverse than, say, ooh - Starship Troopers which is SO limited and holds zero appeal for me. (and there is plenty of scope for joining the military and fighting giant cockroaches in the Dreddverse anyway...)