Well, I don't pretend to be a biologist, but here is how I rationalize what I do:

Personally, I use Q-Tips instead of scent wicks. Why? Because they are cheap, biodegradable, and you can carry a seasons worth in a case the size of your wallet. They don't really waste much, and if you bend them at a 90 degree angle, hang perfectly on branches, or can be wedged into bark of trees.

Reason I don't reuse the drags or wicks is because I figure that a deer's nose is pretty powerful (duh). And I suspect that he can tell the difference between each doe's urine. Just like a human can tell different voices apart, or even mannerisms. I try not to mix the urine of one type of scent with that of another. Sort of like serving onions with apples... they tend to clash a bit. There are all sorts of enzymes and what not in urine that can go bad, or maybe intermix and heck who knows maybe scare off a whitetail. Its just not something worth taking a chance on I suppose. When it comes to washing scent drags... I'd just assume not. I'd rather have the clean and sterile Q-tip than have the chance of a chemical reaction a deer can smell with some sort of detergent and the lure I'm using.

Overkill... maybe.... but thats what I do.