Not aiming to get into a heavy debate barryt but I think that the Y pax have made it clear that they only want the lowest fare and the highest pax requirements are well set out by swedish (above). The actual machine will make no difference and I doubt if more than 5% of pax know what machine they are on.
When the 747 first came out, it did lower seat costs and it did attract people. Then the 767 did the same for the thinner routes but pax began to realise that seat size and the number of toilets was being scaled back. Long haul travel is remarkably cheap now for many Y pax and the a/c are pretty full. It's one thing to regularly fill 7 x 747 for one route in one week but fill 7 x 380? I have no doubt that Singapore will do well with the machine but that is because most of their routes are long (very long) and some have two rotations per day. Therefore, they will be making savings very quickly. For a carrier to take a route with a 74n and expand it to a 380 will take some nerve and a lot of cash.