I think they definitely can work with dressy flats, but I would also wear them with slip on sneakers and something interesting up top -- button-down shirt with a cropped sweater, flowy silk hi-low, anything that is definitely not workout wear. This still achieves the contrast Rute is talking about, but the burden is on the top to push the contrast, if you know what I mean -- and the sneaker is the sleek kind, not the athletic kind, which also helps.
I just bought some skinny sweatpants (which really push the workout wear button), and I plan to wear these with black slip on sneakers and a tailored top, maybe even a blazer. If I can ever afford my dream silver loafers I will wear them with those too.
