Yes, if the flights you purchase drop in price (exact same date and time) and you contact JetBlue, they will issue you a credit voucher towards future flights. I have no idea if they will ever credit back your CC (some people have had SW do this and I know that it's happened at other airlines but few and far between) but if you will fly again, then you can use the credit when paying for future tickets.
I think, however, that we won't be seeing much price dropping in the future (at least not the near future). With gas and oil prices rising the airlines are not going to be dropping their prices unless they are unable to sell their flights out and that just does not seem to be happening. I think you have to find flight days and times that work for you (perhaps expanding to different, nearby airports) and then book it. If they drop, I'll call for a credit. If not, I'm insulated against what I believe will be a definite price rise in the next few months.
Considering Newark for my dates was in the $417 range and JFK was at $237, it's a no brainer. I have to drive and park at Newark anyway, so I add a bit of gas and some tolls to the mix. Still much less than $180/pp in costs.
