Hey I'd say go for it, I don't know anything about modding. Though from what I've seen in the threads, your going to run into a few problems, first off:
Skeletons for your creatures... dwarfs (need a new model), elves (may be easy), dragons (not likely), and some of the other creatures... all possible, but from what I've seen of others creations of fantasy creatures they were more than a little weak.
The rest of the modding is just going to be hard work, though I don't know if you'd be able to "borrow" anything from the actual game that was made for it.... but its a thought, even though the game was piss poorly constructed and worse to play than the movie was to watch...
As for all the opinions on the author being weak copies of something done before... there isn't anything new that hasn't been done before, especially in the written language... so everyone has had to borrow/copy/steal/or reinvent from someone Else's material... that's life or rather literature... For instance... Look at all the mods floating around on this site... very few original pieces around, though perhaps there are a few that some of us haven't seen before that others are calling 'new'...
Personally I like the books, though I thought the movie was poorly done and very rushed, there was a aspect of entertainment there, however brief it may have been.
For those of you who do not like the idea and don't want to help or contribute, I've got this outstanding idea... DON'T READ THE THREAD! It really is that simple... go spend your energies on something positive, like something you do appreciate... be that whatever it may be.