Run an AppleScript by using a keyboard shortcut
A program like Keyboard Maestro can do exactly as you said, but instead of saving the AppleScript as just regular text you can save it as a script (.scpt) and just pass the path to osascript.

A program that I've used off and on that is designed to do this specifically is Red Sweater Software's FastScripts. It's free for up to 10 keyboard shortcuts. Otherwise I've just used LaunchBar (while others would recommend other app launchers)