The Senators lounge at IAD is great, but unless you have over at least an hour or more before a flight, it's not worth the hassle of going over there. You need to take the train back to the main terminal and do Chutes and Ladders up to the people movers to go to D, or continue on the train to the Long March from the mythical land of "future C/D terminal" train station to the C concourse. If you're just going to the A gates, that's a fairly long walk from the LH lounge. Getting to C or D from the lounge is a minimum of 12 minutes or so, longer if you need to go to D.
I gave up my UC membership at the end of 2012, but prior to that, I never used more than a boarding pass to get into an RCC/UC. For international lounges like TAM or LH, I just used my MP card with Star Gold on it. In fact, for the LH lounge at Dulles, you need that card.
As for compensation in the OPs, case, an apology would be nice, and maybe some form of repirmand so that the agent doesn't try it again. That's the main reason to complain; to get UA to fix a problem. Seeing as sky kits are gone and you don't receive anything for broken seats and such on flights anymore, you won't get anything for being denied a few minutes of peace and relative quiet on the ground.