It's moot since the OP is on an I fare, but as to if the J-F upgrade is "worth it" I'd like to note that this may depend on the schedule and length of the flight, along with personal preference. So, if it's an overnight flight and one has trouble sleeping on planes, the upgrade may make it much easier to sleep, and hence be very much "worth it." But an overnight flight for those that can easily sleep in J may not be, since the flight experience might be largely the same either way. Similarly with daytime flights: the better food, much greater ability to work, and so forth, might be very important to one person, and not to another.
There's also the made-to-order ice cream sundaes
