[EDIT][not that anyone is paying attention, but ...]
Looks like this is worth a sending a msg to Todd K....
Well, here we are, a decade later, and ...
Adobe has changed the preferences section name and key a couple of times, I think, since CS6.
According to my plodding and prodding, it seems that these debugger section names need to be checked:
For pre-CC: "Main Pref Section"
For CC pre-2015 (v13.5): "Main Pref Section v2"
for CC 2015 (v13.5): "Extendscript"
and the keys:
"EnableExpressionsDebuggingAtYourOwnRisk" (for "Extendscript" section only)
I may be missing something, but I was able to get AE v13.5 to do the toggling of Script Debugger using the "Extendscript" section name and "EnableExpressionsDebuggingAtYourOwnRisk" key. I kind of missed out on what was and wasn't working during the CC pre-v13.5 era.
The try/catch error block has always been strangely implemented in AE, and this debugger preference behavior was considered a bug that basically never got fixed since it was first noticed and reported. So the workaround was created, and they broke that a couple of times, just for fun.
Just putting this in here to aid anyone who might stumble upon it.
If someone would like to chime in about why these things need to change at all, feel free. I think I know, though, considering how the CC model works, and the rather bad record of backwards compatibility that AE in particular has had.