Lahaina Divers has a regularly weekly scheduled charter to the Carthaginian, as far as I know they're the only ones who DO regularly schedule.
We've done the Carthaginian once, and honestly we both feel like "been there, done that, don't need to do it again". The boat has a bit of marine life on it, there's usually a resident frog fish, but other than that, there's not that much to see. Some folks really enjoy the dive, so it's impossible to say whether or not YOU'LL think it's worth the trip.
Go for it, you'll likely enjoy the dive and then you'll know what you think!