I think it would be awesome if when in the list of viruses to choose, if they had the ones you already own, highlighted or flagged in some way so that you don't pick something you may already have accidentally. Even if you have no previews of what the virus will make you look like, it'd be great to see if you've already chosen the virus previously. It's not easy to decipher some of the names (at least to me) and remember what it created for you in your skins layer.
Just a thought.
"My, my, it would seem you are already a carrier for some of these viruses! The gray names indicate viruses your body has already tried to fight... and lost horribly to. In other words, those are your zombie success stories!"
And then the ones you have skins for already are grayed out or something. I still think you should be able to re-buy them, since some are super fun for progressing. But if we can get partial stages at Rachelle, then maybe even making it so you CANNOT be reinfected with those would be nice.