Now, if you fix your system to no longer be vulnerable the duped key will allow them to keep snooping your files, but personally I think this risk is marginal.
I see two key questions:
* Has the security model has been properly implemented?
* Have its properties have been communicated to the users of the system in a clear enough way that people can evaluate how the risks apply to them?
I don't know about the first question, but on the second they could certainly stand some improvement.
No, this risk is most certainly not marginal.
There is a difference between someone stealing a snapshot of your data, and someone gaining permanent, undetectable access to your data.
It's also about attack scenarios;
With an USB stick crafted for this purpose I could steal your credentials in under 10 seconds, while you're on the toilet and forgot to enable your screensaver. Locating and downloading the actual data would take much longer, planting a trojan for later would be much more difficult and unreliable.