I too have to admit I had visions that had me going, "no, no, not at V&A's", LOL. Anyway, back to the topic, my husband and I had dinner there several years ago, and I don't recall seeing anyone overly frou-frou dressed, although I really wasn't paying much attention to the other diners, as I was just thrilled to be dining there and was having too much fun checking out the decor, the table setting, the menu, etc. I wore a sleeveless black dress, pretty basic, had a few beads on it, that I had bought for a wedding, and my DH wore a basic jacket and tie. So, I think a nice pant suit, or whatever Gwen feels comfortable in will be fine. Just go and have a wonderful time. You won't regret it, it was one of the best dining experiences I've ever had.
OT, but funny story, we were staying at Wilderness Lodge, and not thinking clearly, instead of taking a cab to the Grand Floridian, we took the boat from the WL dock to the MK dock, then boarded the small boat to the GF. This is all in my little black dress, heels, and shawl, feeling like an idiot. I will never forget the looks we got. I'm sure people were thinking I was headed to the MK dressed like that!