Well I actually never noticed that registry setting, even though I have been messing around in that part of the registry quite a bit lately. It's definitely related to the address bar, as it updates every time I resize the search box. However, I can't seem to hide (or even resize) the entire address bar by doing anything to that registry value. So it's probably safe to say that's not it.
The IE6 thing didn't seem to work at all, even in compatibility mode.
I have done plenty of research about people's address bars disappearing, and the only problem with that is I can never find enough information to reverse the process. Generally threads like that just end with the user either doing /sfc scannow, or a re-installation of Windows. If I could find out which file is responsible for creating the address bar, I would at least have a place to start. But I can literally find nothing.
As I said earlier, I would much rather do this in the native Explorer instead of a third-party shell.
I'll keep looking wherever I can, but I haven't been making a whole lot of progress on this, and I honestly feel rather stuck. So again, any information about a system DLL to modify would be huge.