My husband is self-employed, so we pay for all our own travel.

For us, J is worth it (especially when flying TATL), because it means we receive better service from the moment we arrive at the airport, the opportunity to (more or less, let's be real here) relax in a lounge, rather than roam about in a crowded, loud airport (though there are oases -- a steakhouse at JFK's T8 with decent to good food, some lovely shops to peruse at FCO, that sort of thing).

Most of all, there is the more personalized service on board (when that is done right, it's a joy), and, of course, the bed. Ultimately, what you are really paying thousands of dollars for is the opportunity to have a decent night's sleep (often followed by a good quality cuppa or an espresso immediately following), to soften the blow of jet lag, aches and pains to the body after being on a long-haul, that sort of thing.

On a good flight, with good seats and service, you almost want it to be longer. Whether this is all worth the price is, I suppose, a factor of personal finances, as well as what you value in travel (and in life in general). For us, as middle-aged, middle class passengers who are financially stable, the answer is J is a good value for the money, and upgrading to F with miles (or money, when it is a decent proposition) is certainly worth it.

We also fly J when traveling to LatAm, and almost always fly F domestically (but that is for health reasons involving me, so a slightly different, and very personal, decision-making process).