Well, the only other thing I can think of is changing a gadget to "always on top", but I don't think thats what you want. You get there by right clicking on a gadget. If you try that, you can also set the opacity to something low as to still show whats underneath. Only problem with that is if you want to click on something on a window that is underneath you can't get to it. Something to maybe try tho.
I know what you mean though ( I think ...lol ) You'd like a hotkey/combo to show hide a gadget(s) by itself. Haven't seen anything like that. Its not say it can't be done, just I'm not aware of it.
Nice Link, thats about the most thorough one I've seen.
Good Luck, and let us know if you find anything.
P.S. If you can please fill out your system specs, it will really help the members here help you in the future. You can use this link to get to your edit system specs. thnx http://www.sevenforums.com/profile.php?do=extra