Yes, unlike Saavik (whose half-Romulan status is of course non-canonical), T'Pol being 'mixed' would be relevant to the plot and might bring out interesting ideas, e.g. I imagine Vulcans would have to deal with increased anti-pointy ear prejudice, and, perhaps more interestingly, Vulcan society might suffer internal schisms as various individuals and institutions are suspected of being tainted by Romulan influence.
Interesting idea, but how would that have worked with "Balance of Terror" (TOS) establishing that no one knew who the Romulans were before that show? (In the episode, even though Spock thinks that the Romulans are a Vulcan offshoot, he presents it as a probable theory, at best.)