OP: What was it like at AMS on the 26th? The KLM forum has been lighting up about the lines and delays, and I am transiting there myself in a few days (but on KLM). Totally sympathetic about the awful soft product on Polaris. That is a main reason I am not flying UA on this or any upcoming international flights. (Also because there has been no upgrade space and it is more expensive.) And count me as skeptical that the food and beverage will magically improve tomorrow.
Anyway, I strongly suggest Global Entry for IAD if you are eligible. The regular lines can get extraordinarily long in the afternoon when lots of international flights are arriving. Though it may just mean that you have more time to stand by a luggage carrousel to wait for your luggage (which can be totally unpredictable). Also, the pre-check line is in the middle of the upstairs in the main terminal (near the Turkish check-in counter).