If you've already had enough of the game's uncharted worlds and don't really care about getting all the achievements, then no, there isn't a whole lot of reason to replay it. Aside from changing some of the dialogue and opening up an additional romance option, choosing the opposite gender and/or alignment alters very little in the game.
There are five optional assignments that are tied to your pre-service history and Paragon/Renegade standing (which means there are at least 3 assignments you haven't seen), but they're very short and probably not worth a full play-through. If you'd like to make your own decision about whether or not they're worth it, you can find information about all of them in the
Mass Effect walkthrough I recently published.