I'm sure the Hollywood studios would think so, but those who have read the book probably have a different idea. The main argument against a Watchmen 2 (imo), is Alan Moore apparently has no plans to return to the material. Without the brain of Mr. Moore behind it, it would likely fail. Also, Moore planned Watchmen out as self-contained piece. It's pretty obvious that a sequel was never part of the master plan, and there isn't quite enough material to make a prequel that interesting. I have run into some people that think a Watchmen 2 could be made and like I said, Hollywood would if they saw money in it. What do you think, would it be worth it? Would you go see a Watchmen 2 in the theaters?

no 
there couldnt be 
there was no opening at the end for a sequel 
so nope 

Hell fucking no. What would it even be about? It would be the worst comic book film of all time, even doing the impossible and sinking below Batman and  Robin levels of suckage

unless Moore writes another novel no, even then its not like they follow the novels that closely.

For a while there were news articles saying that due to reorganization of DC Comics the new management wanted to expand the Watchmen franchise. Most people assumed that meant a sequel. Dan Didio confirmed that it would not mean a sequel and they were just looking at how to leverage the franchise.
 
 http://io9.com/5475616/dc-says-no-to-watchmen-2-+-but-leaves-door-open-for-superman-sequel
 http://io9.com/5464663/watchmen-sequel-not-a-chance-says-hollywood