On my flight from London to New York last June, I was upgraded to World Traveller Plus. It was certainly more comfortable than Economy, no question. In particular, the seat had an extendable leg rest that made sleeping easier. AS you are both flying on considerably longer flights than mine, that may be particularly useful. The actual service is identical to the regular Economy section, though. Ultimately it depends on the price differential: are you willing to pay the difference for a more comfy seat?
Also, if you are flying alone, definitely go for the solitary seats in the first row, just behind doors 4L and R. You get a lot more privacy and legroom.