I am not going to rate it on a scale from 1-10 but I will tell you what I think. It's honestly not going to matter if you have decks inside a wooden or plastic drawer, or in a cardboard box. As long as where you are storing the decks is does not have a separate range of humidity from the rest of your house, it is not going to matter whether they are touching plastic, wood or cardboard. Change in humidity is the only thing that is going to warp decks, so just keep them in a neutral environment.
I have mine if frames simply because I like how it displays them, not because it has some ability to make keep them in pristine condition, although since they are in view at all times it makes it easier to remove dust and such. But I don't allows sun to shine through onto them in the morning, might be a bit overprotective but what ever.