Yeah, if they already go to sleep at 3-4 in the morning I guess that shouldn't be tampered with. I reckon that with the scripting already there it perhaps was originally planned to have the streets empty in early hours, that is until those scenes came along where that woman gets attacked upon entering Markarth for the first time, and some one gets their head chopped off upon entering another city for the first time (can't remember the name off-hand).
Are there any dungeon repopulators out there? I've done Bleak Fall Barrow on new playthroughs a number of times now it's become a kinda' chore.
I'd love to see a draugr dungeon with added variants such as skeletons/zombies. Draugr retexture to add a number of differing draugr, and a new armor set that can be looted from the draugr, something like rusted iron chain or plate that has frost resist enchantments.
Skeletons could be the usual, then a tougher variant that can only be harmed by magic/silver that has poison ability (or something along those lines), and something like a boss skeleton (bone king/queen skeleton) that uses frost attacks, can be looted and will always have a circlet of fortify something or other.
As for zombies, they could be few and far between, unfortunate adventurers that only got so gar into the dungeon. Perhaps the reason why you haven't found any loot yet is that some adventurer had already crept along the darkened passages and pocketed most of the loot, only to meet a grisly end in trap or an impassable wall that needed the claw key. The walking corpses are slow but tough, using disease and melee, but the loot on them (apart from the stuff they've already picked up through the dungeon) is mainly useful adventuring gear. Remove all the foodstuffs from the dungeon, and repopulate the chests etc with gems and gold, not loads of heavy weapons that become a pain to have manage (weight wise) in your inventory.
I'd love to see a mod like this. Perhaps if I get the time, I'll look into learning how to put something like this together myself.