I would have suggested Udvar-Hazy, but you FI doesn't participate in Pre-Check and you are in the back, so not even a priority lane at TSA. Those lines can be monumental so you really need to be checked in and headed for the checkpoint no later than T-90.

While you won't find anything with a Michelin star or two at IAD, there are a significant number of decent places to eat where you can hang out and have a nice slow meal and spend a lot less than you will on a lounge.