This argument seems to me to be a variant of the “toothbrush argument,” the argument that to preserve your health you need to replace your toothbrush every few months becuase it gets covered with germs from your mouth. This makes about as much sense to me as periodically replacing (or sterilizing or even cleaning) the shovel you use to clean out your chicken coop becuase it gets germs on it.
Eleusis is right, you discussed a saturation point which implies a ratio of the thing that is doing the saturating to the thing that started out not being saturated. If you can’t see the connection between ratio’s and the word saturation then I have to wonder what you are really trying to say when you say “saturated”.
My personal experience experience leads me to believe the spores make a difference, although, understanding that I can only see the tip of the iceberg I’m certainly open to be wrong.
However, if you read popular newspapers and magazines or browse the internet you will find many examples such as this: “Make sure you replace your toothbrush regularly, over time bacteria build up in the bristles and this means that every time you clean your teeth you are adding more bacteria to your mouth not removing them!” posted at http://www.craigentinny.co.uk/resources/ohselect.htm
It’s like spraying your shoes with disinfectant after walking on the lawn so that you won’t track fungal spores back on to it the next time you walk across it.