I've given it a great deal of thought (not having a life can do that to a person
), and IMO what Nemesis really
needed to work with that story is for Shinzon to not be Picard's friggin' CLONE.
Look at it this way: North Korea. Imagine Shinzon as Kim Jong Un. He's the cocky young heir apparent to a long time nemesis of the Federation. There's been a spill in the Romulan senate and this new guy has become praetor. The Feds know nothing about him, and are cautious about what his true motives are, especially after he makes an offer of peace. All of this is exactly as seen in the movie, but where the plot splits with the established script is that in this version Shinzon isn't a Picard clone, but rather a genuine Reman... or possibly even a Romulan. The movie takes a more political flair, and Picard no longer has a 'personal' stake in the plot. Rather, he has to act as a professional diplomat, immediately aligning him to the Picard character as seen on TV. The plot could go in any number of better directions from this setup than it did in the actual movie. Shinzon being Picard's clone is a major headache in the existing script and makes a mockery of Shinzon as a villain (and Picard in the process too).
Instead of being a souless action shoot 'em up, instead Nemesis could have been an intriguing political drama... all without changing too much about the fundamental story setup. And with Shinzon being radically unhinged, they could still
have worked some action scenes in to keep the popcorn munchers happy. Win/Win.