Well, the Red Samurai katana probably always has a Personalized Grip, giving it +2 Accuracy. But remember that while they say Samurai, these are Corporate Security elites. The katana is largely ceremonial in use, since they do have, and use, firearms where appropriate. However, it is made functional, so that they can use it if pressed or in dire straits.
As for the stats, if you're running over the 6 or 7 successes needed to hit the limit consistently, then you probably have enough dice to start dropping a couple for some called shots for extra damage or effects. Also, AP becomes more important when dealing with Hardened Armor, like milspec armor or some critters, and is certainly a deciding factor when dealing with Spirits. Each point of AP reduces both the amount the DV is reduced, and the number of auto-hits the critter gets to resist, making it much more likely for your nonmagical blade to hit them.