Believe it or not people aren't so collectively stupid they can't figure out who someone is just because they haven't watched all the material they've appeared in.
I watched ST3 before I watched most of TOS... I was still able to figure out who Sarek was.
Not that I'm a big fan of the proposed storyline. There was nothing wrong with using Romulans as the villains.... except that's really not what they did in Nemesis. You want a Romulan villain, have Tomalak, who was disgraced by his lost encounters with Picard, despite a sterling record in the Dominion war was refused promotion, and leads a military coup against the government.
Then you have a villain that has a real motive against Picard and the Federation, with some backstory, while not overwhelming to a newcomer, that would enhance the characterization.