I don’t really think the task would be that menial. It would take probably less than ten seconds to clean your clothes, and you could find or craft soap easily. I mean, you instantly repair your clothes, craft items, butcher corpses, and sleeping for 9 hours in-game takes about a minute on a slow computer. Using the word “menial” to describe anything you do in Cata is pretty weak, because basically everything you do in-game is the result of choice by you, the player, and basically all of the “menial” aspects of the game are streamlined so that the player doesn’t have to deal with them, the character you’re playing as does. Cleaning clothes, items, and weapons and everything that came along with it would be streamlined just like all of the other “menial” tasks in the game, and it would add a level of realism and interest on par with damage to items. It’s not unreasonable. If a damaged shirt is problematic for the survivor then it just seems logical to me that a dirty shirt should be problematic as well.
Towards the endgame, what you’ll find is that your long-surviving player has stacks of clothing in perfectly good shape, and has no need to repair damaged ones if you are near your base, you can just ditch the clothes, backpack, or item and get a new one, or save it simply to scrap for whatever material it’s made out of. To distinguish between clean and dirty clothes, weapons, and items would make people less likely just to hoard a crapton of items and clothes and weapons, because you would take better care of the items that you were using and were important to you, and if it was just another item to stash in your base, you’d be less likely to take it because you’d have to go through the cleaning process to make it an item that you’d want to keep. Just like you wouldn’t pick up a shredded t-shirt in the world unless you needed it for some reason, you wouldn’t be as likely to pick up a dirty one. Items that aren’t damaged are more valuable than the same items that are damaged, and likewise, clean items would be more valuable than dirty ones, for the same reason.
Adding this quality would make it more rewarding to raid higher-level locations, because they would have cleaner items and you wouldn’t have to clean them.
I personally like raiding locations, and having a quality like this to items would make me consider more whether I wanted to take it or not, knowing I’d have to clean it once I got it back to my base, and would stop me from hoarding items.
Furthermore, it would make the items that are special or important to me more distinguishable because they’d be clean. Sometimes I’ll find myself in-game with a stacked armory full of weapons, sometimes with two or three of the same gun. If they could get dirty, then they’d be different from one another even if they were the same gun, and I could just swap a dirty gun out for a clean one of the same type instead of cleaning it. The player would be more attached to items that you’ve maintained over time, and less attached to new items that you find in the world.
Besides that, it just makes sense to me. Sometimes in-game, I’ll just stop and think, “Shit. I’ve been wearing this t-shirt for three months and I haven’t cleaned it at all,” yet, the shirt is just as good as one I shoved in a locker three months ago. That doesn’t add up for me, and it removes a level of realism from the game that I think would be interesting and just downright reasonable to have in the game.