Unless sold out, US requires coupons for upgrades. Are you so committed to IAD? BWI is a great airport and a lot easier to navigate, but it depends on your geography. Love IAD going to Reston and catching the Hyatt shuttle. Online e-ticket changes are not that difficult, but get all of your boarding passes at initial check-in. Don't play segment roulette! You may get stuck somewhere long enough to qualify for residency.