I don't know how to advise you on this one!
I can tell you straight up that two videographers is desirable, in order to cover the main angles, but video is different from photo. Each video camera is stuck to one position in order to get a stable and continuous shot, whereas a photographer can run around.
For mid-tier, high-tier weddings, two photographers, or at least one photographer + assistant, is pretty standard. But I should say that, for most weddings, including large ones, one photographer is usually fine.
It's easier to say what the two photographers would be doing than to say whether it's the better choice.
- Sometimes, they're in two locations at once, like bride and groom's house. (Otherwise, if it's just a single photographer, they'd usually go to the groom's house first, and then to the bride's.)
- Sometimes they're shooting two angles at once, like bride coming down aisle + groom reaction. But even then, it's possible for a single photographer to go click-click-click on the bride, and then spin around to get the groom.
- Sometimes one is using a wide angle while the other is using a close-up.
- Sometimes one is focusing on the safe and expected shots, while the other is running around getting creative/interesting/candid shots.
- Sometimes one photographer acts more like an assistant, holding a flash or a reflector, or adjusting buttons and clothing (to tidy up the "school photo" group shots).
- Sometimes it's about efficiency (eg, one photographer getting shots of the guys at the post-ceremony photoshoot while the other gets shots of the girls).
- And sometimes they're doing pretty much the same thing (for instance, running around a dance floor getting shots of guests), so basically what you're paying for is greater quantity of photos -- or more safety, reliability that you're going to get the shot.
I guess how much you like the photographer's work is the main thing; and if he or she is telling you there were two photographers needed to capture a particular wedding you liked in their portfolio, with that quality of photographs and that quantity, then maybe two isn't a luxury as such, but just the cost of getting it right.