So if what you used contained your wallet data at any point in time, wipe them, but kept them... just in case.
It did not contain wallet data as such. It contained mnemonic seed displayed on an offline Linux machine within vetted Javascript pages inside Chromium webbrowser. The question is: poses such a thing a potential security threat?
If an USB is plugged in a machine that is connected to the internet, it is safe to be considered compromised. Call me paranoid, but there is no such thing as enough paranoia when it comes to bitcoin, got to stay safe.
I wouldn't be using seeds for offline storage. Maybe Armory is the best solution for offline storage, since you keep the private keys separate like on a wallet.dat file (I think).
The point is to not have all of your money on a single seed that would give access to an attacker to all of your money. So don't use Electrum to manage offline cold storage for example, since it uses a seed.