Now I have root access _only_ through the adb shell. None of the apps (including Superuser.apk itself as tested by updating /system/bin/su) can get root access, yet I have no problem running root through an adb shell - remounted file systems, even performed an su which is the only instance Superuser.apk's log shows. Root access in the shell remains between reboots, so it's not a temporary root.
If the adb shell has root, I _should_ be able to use it to grant access to everything else, and I've followed a few different "manual" root instructions (having different permission settings for su and busybox), with no joy. So long as I connect with a USB cable and type on the Windows machine, I'm god. On the tablet itself...not so much.
I hope that someone with a more intimate knowledge of Android internals can point me in the right direction for achieving root completely. Currently have Titanium Backup and ConnectBot (long java errors when I attempt to su there) installed to test root, Superuser v3.1.3 and su v3.1.1. Permissions on su are -rwsr-sr-x. And the human is confused.