Note that, despite what DL calls it, this flight will not have a true business class section. They call it business class but it is really domestic first. The premium cabin on domestic flights that share flight numbers with international flights is called "business class."
Whether it is worth it depends on the time of day, nature of your trip, etc.
On a trip that I know is going to be hectic, first is worth it for the relative calm that the cabin provides. On a trip to a vacation spot (Hawai'i comes to mind), definitely no.