OP, I'm sorry certain posters are being unhelpful and piling on. It happens a lot on these boards. Don't let it get you down.
100% this.
Regarding your actual issue, if the new airfare is "only" $640 versus a $1,200 fee to change your original itinerary, than it makes sense to spend less to book the new tickets. If you go that route, then make sure you Cancel the original flights, so that there are no issues from the airline seeing that you have (in their view) "duplicate" tickets. When you cancel, those tickets will still have value according to Jet Blue's rules, and you can always use them before they expire if you pay the change fee.
Also keep an eye on schedule change on your original flights, that can be a lifesaver. In general, airlines will be far more likely to waive change fees if they change the schedule after you have booked.
Another option is the HUCA strategy. HUCA stands for "hang up and call again". Call and ask nicely for the favor of waiving change fees. If they say yes, great! If they say no (as we would all expect), then politely say thank you, and hang up without arguing or trying to persuade the rep to help you. Call again, and ask again nicely, and repeat as necessary, if desired. The goal is that one of your calls will find a sympathetic rep who will waive the fees. Never act entitled or demanding, and always throw yourself on the mercy of the rep. Worst case outcome is that you still have to pay the change fees, but the best case is waived change fees. Outcomes with this strategy are obviously all over the map, but, IMHO, it never hurts to try.
And yes, I am tired of many of the changes that airlines have made, especially with increases in change fees. Airlines don't raise their change fees by $50 because they incurred a $50 increase in cost; it is mostly pure profit.