I would have cut Shinzon's creepiness. I just don't think he needed to be totally evil. He could have just captured Picard to take non-death threatening blood transfusions from him. Maybe it would have been better for him to try to destroy Romulus and maybe Picard would seem nobler if he was trying to save the billions on a planet he doesn't really like. Maybe he would sacrifice his only son (and Data to do it).
I dunno about making him Picard's actual son, but I'm in agreement with some of this. I wish they'd made Shinzon a more complex character than ending up Obviously Evil. So while I'd want to keep his conflict and rivalry with Picard, somehow, I'd try and avoid the bit about destroying earth. Have him on some other dark and destructive agenda (maybe against romulus) and Picard trying desperately to pull him away, because Picard knows he must have some goodness inside.