I have saved 1,500 Dream points and then spent some of them. What can I do with the remaining balance? Do I need to save until I have 1,500 Dream points again?

To start using your Dream points, you need to save until you have 1,500 of them only once. After you have done that, all your old and new Dream points will be active, regardless of the balance. All unused dreams remain on your account and can be spent any time.