Make each city/province a character, if you wish, so owning more cities would present more problems within the game. Just an idea.
Noooooo, it's hard enough to keep track of characters and their relations as it is; it will be much harder if so many more governors are needed.
I think Rome 2 should go more in-depth character-wise, with the Monarch, or the Leader of the year, able to propose marriages to secure alliances; but I don't want CK2-type depth, though family ties should be considered. For example, THE Julius Caesar's family was perturbed that he would prosecute Gaius Antonius Hybrida, the husband of Caesar's THIRD-cousin Julia, in the courts. That Julia's brother Lucius Julius Caesar didn't hesitate to prosecute her NEXT husband, Publius Cornelius Lentulus Sura, during the unfolding of the Catilinarian Conspiracy; she hated him after that, of course, and it was only the depth and ignominy of the conspiracy that saved Lucius Caesar from general scorn.
So, you see, even such distant ties are important.