DL offers EC at a 50% discount for Alaska Golds for international flights, and 25% for MVPs and DL Silvers...
EC is a little nicer than E+ on UA since the seat has a touch more recline and free booze.
But, the EC experience definitely will not trump the ability to use a SWU and upgrade to C. I think the SEA-NRT flight uses the lie-flat 777s more often now, so that definitely beats sleeping upright
ETA: Mis-read and realized that you are flying to BKK... That is a long way to go. I would rather purchase a W fare and use SWUs since SEA-NRT is a pretty easy upgrade and BKK might be a little tougher, but most of the time it should clear.