Let me provide additional things to think about.
First, it is not really $750 off. That is before SSS and onboard booking discounts and also TA discount. If you think of each of those as 5%, that is closer to $650 off.
Second, don't forget taxes (I think around 10% in new york) and breakfast (I think a hot breakfast at Oscars which is around $20). Don't forget trasfers, around $30 each way to LGA, more to JFK if you decide on Jet Blue. Theater tickets are closer to $80 to $100.
Third, don't forget restrictions on non-refundable tickets. If you cancel your cruise (pre-penalty), you don't have to pay air if through cruise line. However, you are stuck with your own tickets. Also, it is usually easier to change around cruise air (just like wiht ff tickets) than it is to change cheap tickets.
Of course, buying own tickets and hotels EARNS points and miles, which have some additional value.
I don't know which is the better deal. I just wanted to point out additional factors.