My wife and I flew Delta on Feb 4 JFK-TLV and then back on Feb 13. Since it was such a long flight we "upgraded" to Economy Comfort for $119 each per segment. Was it worth it?
#1 - the seat does recline more and you have some more leg room - worth it because it was a very long flight otherwise no.
#2 - the with of the seat on the B747-400 is the same as in regular coach and it is very tight, so Economy comfort does not makes any difference in that respect
#3 - service - not worth it. Delta advertises that they will provide extra service i.e. free drinks, that did not happen. The service was awful!