You can't just add 2-3 weeks to a deadline and hope for more entries, you only do extensions of like 1 week for people who are already working on their stuff to finish up. You might as well just be milking the community for entries at this point. Just extend for like a week for DvO and that other dude, then close it.
Also, contests existing should depend on the number of completed entries for previous contests of the same type. If only a few people enter special effects contests, then it is obvious that in the future the contest isn't really worth existing, since it'll just feed the same people rep over and over and over again. It's okay if something isn't popular, really; if the community truly wanted this kind of contest, there'd be more entries by now.