More Romulan classes of ships, rather than just the D'deridex.
Commander T'Rul returning to DS9 to act as liaison (the Romulan equivilant to Martok).
I completely agree with this, and it's something that I've always wondered about. The Romulans were part of the alliance with the Federation and the Klingons, but the writers didn't treat them with the same level of respect. Granted, the Romulans didn't have the same relationship with the Federation that the Klingons had, but it would have been nice to see shots of Romulan ships orbiting Deep Space 9
, instead of the stock footage showing only Federation and Klingon vessels.
It would also have been nice to see more of their troops wandering the Promenade or eating in Quark's. The only time Romulans were shown on the station was during the scenes involving war planning and strategy, or those few scenes with Kira and Cretak chatting on the Promenade.