Yeah, the 3730 is actually helpful in that it "lines up" perfectly with the regular 3700 (at least before they changed the latch sysem) and it gives you a deeper slot (har har) to put the larger figures in. I don't see this case nearly as often as the other models, but out of the way K-Marts often have them lying around at bizarre times of the year. This time of year is also the best time to be picking the Plano cases up, as sporting goods sections are stocking a lot of fishing equipment and this type of case is in demand from both the target market for such things, and from action figure collectors.
I also thought I would post and let everyone know on who will and won't fit in the cases. Not everyone will lay flat in the 3700, but I've managed to get all the Amidala figures into the regular 3700 case without fail. That said, here's who won't fit in the 3700 whatsoever, and what cases they will fit in:
POTF2: Darktrooper (3730, 3750), Muftak (3730, 3750)
TPM: Graxxol Kelvyyn (3730, 3750), Darth Maul (from Tatooine Showdown Cinema Scene; 3750)
Saga 2002: Shaak Ti (3730), Dexter Jettster (3730, 3750), Luminara Unduli (3730, 3750), Ephant Mon (won't fit anywhere), Deluxe Mace Windu (3730, 3750)
Saga 2003: Mace Windu (3730, 3750), Chewbacca (from DS Trash Compactor set; 3730, 3750), Barris Offee (3750, but only with cloak removed and placed alongside her)
Clone Wars: Rodian and Human Jedi (from three pack; 3730, 3750)
Clone Wars Animated: ARC Trooper (3730, 3750), Count Dooku (3730, 3750), Durge (3730, 3750), Asaaj Ventress (3730, 3750), Obi-Wan (3730, 3750), General Grievous (3750, but only after removing his head)
Saga 2004: Rappertunie (3730, 3750, but this is if you want to keep his harmonica and base with him), Budo (3730, 3750)
ROTS: Deluxe Darth Sidious/Palpatine (3730, 3750)
I've also found that the 3730 is an excellent case to hold accessories that are larger (such as Big Ass Cannons) and to keep stuff from the accessory packs (TPM or Saga) together so they won't get mixed in with regular figures. They also work pretty well for storing bases, but a lot of times, I just use a regular Rubbermaid container to hold all of those.