The Twilight Sage has a huge fan base so the market is definitely there for more books to be added to the series, the series could always be revived with a different storyline that takes place completely separately from where the last book let off, I believe that most authors will not return to a finished series though.
Yes, more books should be written in the Twilight Saga, because they would sell. If people are willing to buy the books, the people who write them should sell them. It is creating something that doesn't exist before, and if there is a market for it, the person can save the money or they can give it to charity.
No, I don't think that any more books should be written in the Twilight Saga. And neither does its author, who appears to be content to ride off into the sunset in a giant semi trailer filled with the tons of cash she made from her little enterprise. The books and moves, by the way, were terrible. Let's never speak of them again.
There should never be another Twilight Saga book written again. What a terrible series and what a ridiculous take on vampires. I understand wanting to make twists in traditional stories, but Vampires that sparkle in the sun? Really? I wish this series never got so popular. It was so awful.
No, after the first i do not know six books or how ever many they have out now they need to just give up on it, and not keep going trying to beat a dead horse. I think that these books and movies are done not and they need not more.