A romantic dinner is probably defined differently by different people. For us, we would not consider most regular TS restaurants as romantic. The theming might be nice and the food might be good, but they are usually crowded, noisy and crawling with ankle biters. A couple of possible exceptions might be Spice Road Table, Sanaa, and a Rose&Crown patio table, especially if you get a late reservation.
Even with the signatures, some are loud, with an abundance of kids. I have nothing against kids. Have some of my own. But they aren't exactly conducive to a romantic meal. So I'd avoid California Grill and Narcoossees for that reason. The Swolphin signatures are good, and for Disney signatures we like Citricos Jiko, or Artist Point, especially with a late (after 8:00) ADR.