Only one thing left to do: write my first AppleScript. Since I'm a rank amateur, suggestions and helpful critiques are welcomed.
tell application "Safari" to activate
tell application "System Events"
if (system attribute "sysv") < 4144 or UI elements enabled then
tell application process "Safari"
-- open Preferences window
click menu item "Preferences…" of menu "Safari" of ¬
menu bar item "Safari" of menu bar 1
-- window title varies according to type of Prefs initially
-- selected, so save to a variable
get value of static text 1 of window 1
copy the result as string to varWindowName
-- switch to Security Prefs
click button "Security" of tool bar 1 of window varWindowName
-- toggles JavaScript checkbox
click checkbox "Enable JavaScript" of group 1 of group 1 ¬
of window "Security"
-- get new state for confirmation dialog
get value of checkbox "Enable Javascript" of group 1 of group 1 ¬
of window "Security"
copy the result as number to varResult
if varResult = 0 then
set varResult to "OFF"
else
set varResult to "ON"
end if
-- close Preferences window
click button 1 of window "Security"
-- display confirmation dialog
display dialog ("\"Toggle JavaScript\" script confirmation:" & ¬
return & return & "JavaScript is now " & varResult & ".") ¬
buttons {"OK"} default button "OK" giving up after 7 with icon 1
end tell
else
tell application "System Preferences"
activate
set current pane to pane "com.apple.preference.universalaccess"
beep
-- NOTE: The following section has a hard-coded return between
-- 'Universal Access' and 'preference pane'. Replace it with a
-- single space.
display dialog "GUI Scripting is not enabled." & return & return & ¬
"Check \"Enable access for assistive devices\" in the Universal Access
preference pane (authentication is required), then run this script again." ¬
with icon stop buttons {"OK"} default button "OK"
end tell
end if
end tell
For maximum efficiency, save the script as an Application using Script Editor, and use in combination with Quicksilver / LaunchBar / Butler / Whatever. BTW, I would not have been able to write this script without the assistance of PreFab Software's UI Browser.

