Might be a good idea to look at the sites of the airlines you're interested in, as it probably depends a lot of the airline(s) in question. E.g. on some airlines it might mean the difference between a slippery slope lie-flat and a true flat bed, whereas on some you get the flat bed anyway (and how big a deal that is, probably depends on whether its a redeye or not).

Although, I think most would agree that if paying cash, it is not worth it. I don't consider sitting in J that tough a job that I couldn't do that for about $1000 an hour (e.g. JFK-FRA-JFK LH J about $3300 F about $15500).