The more time I spent on this, the more I feel there isn't a simple answer to this question.
In some fields, such as political philosophy, students are encouraged to read the original works such as Leviathan.
In the other extreme, in biology, almost no one reads Darwin's original book. Whatever he has discovered is (assumed to be) subsumed by subsequent textbooks.
Now, this is usually not due to trying to do justice to Hobbes -- I don't think we care about him per se, but only his thoughts. Then, why can't his work be put aside and summarized in future textbooks, just like Darwin's theories?