Well, what I have made so far is exactly what you describe except for the fact that the files are locally stored and not linked.
I do like the idea of linked files to create a bigger collection, but we have no control at all about the files hosted at other locations. A lot of files are hosted at Brickshelf, how long does Brickshelf still exist? A lot of files are hosted at Dropbox, what if a user deletes or moves the files in dropbox? etc. etc.
So, I highly doubt if it would be useful to include links instead of adding the files themselves. It could become very annoying when you'd like to download a file a year from now and the link doesn't work anymore.
I do like the idea of linked files to create a bigger collection, but we have no control at all about the files hosted at other locations. A lot of files are hosted at Brickshelf, how long does Brickshelf still exist? A lot of files are hosted at Dropbox, what if a user deletes or moves the files in dropbox? etc. etc.
So, I highly doubt if it would be useful to include links instead of adding the files themselves. It could become very annoying when you'd like to download a file a year from now and the link doesn't work anymore.