Thing is, where you see a problem, I see Andreas Katsulas. Promote Tomalak a notch or two and put him in charge of 'nefarious Romulan schemes unit'; and he'd fit in nicely with Sela's role. Yeah it's a cheat having a major Romulan player like that, but the Klingon Empire benefited from having Gowron and the Cardassians would benefit similarly in DS9 with Dukat. It makes the world smaller but it makes the drama more, well, interesting.
OK, not a problem as long as it's clear that Tomalak's been promoted and/or reassigned to heading up the BMF (Bureau of Messin' with the Feds?

Even so, there were more Klingons running around TNG than Gowron, and we did deal with different Cardassians from time to time, so why not more than one Rommie? Tomalak could be promoted and start doing homeworld stuff like "Unification", but then we'd need a new Rom to run the warbirds that were always getting in Picard's face.