As the title says, I'd like to be able to find whether an APK has debuggable set to true or false on a computer without having to install it on the device, run it and see whether it shows up in DDMS or not.
This is one of those "easy once you know how" things - Use the aapt tool to inspect the manifest.
aapt dump xmltree YourApp.apk AndroidManifest.xml | grep debuggable
That command will give you a dump of the compiled form of the AndroidManifest.xml file- the output will look something like
A: android:debuggable(0x0101000f)=(type 0x12)0x0
(Actual output from my command prompt) in that example, the 0x0 indicates false.