I think this chapter just proved that someone, most likely Quirrell, has modified Harry's memory. Remember how Harry easily figured out how to quickly make large sums of money by trading gold and silver between the wizard and muggle markets? And now, he doesn't seem to recall that brilliant insight when Hermione mentions that they need a way to make lots of money fast. Moreover, the occlumency teacher with whom Quirrell set up a lesson (possibly Quirrell himself in disguise) mentioned that he would like to be able to remember that same trick after he read it in Harry's thoughts. Clearly, whatever the villian is planning, it requires Harry not having large sums of money.

The creation of a philosopher's stone would, therefore, pose a direct threat to this plan. Hermione is in even more danger than before.