Sadly I lost my keystore, so I tried some things out. I was using 0.8.2 at the time and lost %AppData%\Roaming\Ethereum, but %AppData%\Roaming\Mist is still there in one of my backups. So when I use the old 0.8.2, and substiute the %AppData%\Roaming\Mist my old account shows up for a second till the GUI updates to the "new" keystore situation.
At least I have a screenshot from what I lost now.
And yea, the obvious question: any recovery possible based on the %AppData%\Roaming\Mist? Maybe somebody reversed engineered his keystore from that folder?