And nobody ascends to the centre seat of a Romulan warbird by being stupid,dullards don't tend to last long.
Perhaps Tomalek's ambition simply exceeded his ability.
As for recasting Tomalek,it would of course be possible(Peter Coyote would IMO make a great Romulan)but Katsulas had such tremendous presence that it is his face I see whenever Tomalek gets a mention.