I made a few more modifications since I last posted. I did a complete overhaul of the crane/winch system (inspired by Carp's mods). I wanted a winch that could stay attached to the body of the AT-AT regardless of if the exterior panels were on or not. it folds nicely into the body of the AT-AT on both sides of the model and has good stability. I also added seating for my scout troopers in the speeder bay (had to remove a plate or two from the exterior armor to achieve this), as well as "cargo" (listed on the UCS plaque) with Imperial insignia in the empty space in the engine room.
I really liked the idea of a "door gunner" to cover deploying troops that someone mentioned here, so I used some old playscale AT-AT driver minifigs and a modified e-web to achieve that. The base lighting kit is from "Light My Bricks" but I've made a number of additions there as well-- mostly in the speeder bay and the engine room.