I think the last comment by Florin is very well articulated. It is always a personal decision, and that has to be worth to you.

In my case, I'm a heavy sleeper, and I can sleep anywhere. Give me an eye mask, a noise cancelling headset and a "do not disturb" sign on my seat (I usually ask the flight attendant not to wake me up for food), and I can sleep for the whole flight. When changing timezones, I plan my sleep in order to reduce jet lag, and I'm seldom suffering from it on my arrival. This is to say that I can sleep almost as well in Y than in J, and the flat bad and the lounge are really the only things I care about in J, but I already get the lounge access because of my status on the airlines I fly often. I also fly quite a bit on J for business, and in those cases sleeping is also super important to me. I seldom eat J meals because I want to prioritize my sleep to arrive fresh at the other side, which means often the right time to sleep is at the beginning of the flight (while dinner would be served). About meals, in most cases it is something better than Y but still tasteless that I can get for $30 at the airport before the flight, or for free at the lounge, or I go for a $80 meal and expense to my company anyways.... and in any case board the plan ready to sleep. Flying back home over the weekend vs. flying out, as well as red-eye vs. day flight, both have a role in my decision if the upgrade is worth or not. So, in my case, anything more than a few hundred dollars for the whole flight is not worth.

And as you can see, all the above is super personal.