If you have to ask, then its not worth it. Very few people can justify the absolutely insane cost of Upper Class. £3000 return for a plane ticket to the USA is enormous money. If you need to ask us whether its 'worth it' then it almost certainly isn't.
I fly Economy with Virgin every time I go to the States. To be honest, you get a seat, its reasonably comfortable, all your meals are included and you can sit and watch movies. It's not as nice as Upper Class by some margin but then I paid £470 return to Los Angeles and not £3000.
Unless I was so wealthy I simply didn't care then I'd always be able to find something better to do with that £2500 saving. Even if it fitted my holiday budget I'd rather spend it upgrading hotels than on my flight. Given your first night in your first hotel is longer than the entire flight..