I've let this ride, and not said anything about the topic, although I had thoughts, but was trying to marshal them into some sort of order so I could say what I think.
Washed out baits may work on a couple of levels;
The bait has been in the water for a couple of days, so it is safe to eat and not a pressure point that the carp feel they are eating freshly put in bait. If the pressure is so high that they don't eat baits that haven't been in the water a couple of day, then older 'washed out' baits may be the ones that are safe. It may also be that they would eat fresh baits if the amount of bait going in was enough so that they felt safe, whereas, they are leaving the new baits as they simply aren't safe.
It may also be that fresh baits could possibly be overloaded with flavours, and at introduction levels are so high that they repel!
I used to feel that on many high pressure weekend syndrome lakes, the fish do leave the baits introduced on Friday until Sunday at the earliest, and those that catch are those that are using washed out baits, small stringers, or even single hookbaits, different from those fishing over the large amount of spodded baits.
If you prebait with enough bait that the carp are comfortable eating it, then I don't think that washed out baits are an advantage, and for my weekend trips, I do try to be different from the 'norm'. However, I do also think that fresh baits can be a danger to fish, and so I often use an older hookbait. I may start the trip with a hookbait, and use that same hookbait for a couple of days if it doesn't get pulled off the hair (fish or deterioration, which can be reduced by meshing hookbait ). I also bait up with fresh baits as my freebies. The hookbait is 'safe', the freebies are fresh and dangerous, the hookbait catches 'em.
Also it can be worth leaving a bait in place for a couple of days, again, you have to have confidence that it will stay on the hook/hair.
A few years ago, this washed out bait thing, I watched the carp ignoring sweetcorn that was fresh, until it had started to go a bit grey after a couple of days. The tench and the bream would eat it fresh (until a few were caught on it), and then they would avoid the area for a few days, (tench especially), but for the carp to take sweetcorn, it had to have been introduced a couple of days previously.
My main belief is simply that baits get left over a weekend, due to weekend syndrome, and a washed out bait may be better, but if fishing normally (midweek), pre-bait as much as possible, and you shouldn't need a washed out bait, except at the weekend when the pressure is usually highest