I don't understand what you mean by saying that submitting art and stories won't make the site better.
You have tons of cool content that you will put on the site, but you can't have an endless amount of it, because The Dig is such an old game. Sooner or later you will run out of updating, unless people are encouraged to submit their fanworks and other possible content.
Besides, having an active fan base that posts their own work will keep the site alive, even after the "Ooh, aah!" of your content has passed. When a newbie comes to the site, sees that many other fans have posted their work and got extra (like the points) for it, they will naturally feel like posting something as well.
Encouraging fans to participate (and what can they do, except post fanwork?) creates a friendly atmosphere and we can all be best buddies and forget the kind of silly arguments we had earlier.
But believe me, saying that the fans' participation won't improve the site is a certain way to make sure that no one wants to submit anything. It gives the feeling that they are not appreciated, and at least some of them will go away once they have checked out everything that you have put up. I know, because I had planned drawing some art for the site. Now that I know what your opinion on that is, I'll probably draw something for Razputin's Domain instead.